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IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS)

IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS)

AVISO DE MODIFICACIÓN DE SALARIO INTEGRADO ANTE EL IMSS

Conforme al Artículo 34 de la Ley del Seguro Social

I. DATOS DEL PATRÓN

Razón Social / Nombre del Patrón: [Employer Name]

RFC del Patrón: [Employer RFC]

Registro Patronal IMSS: [Registro Patronal]

II. DATOS DEL TRABAJADOR

Nombre Completo: [Worker Name]

Número de Seguridad Social (NSS): [Worker NSS]

CURP: [Worker CURP]

RFC: [Worker RFC]

Puesto de Trabajo: [Job Title]

III. DATOS DE LA MODIFICACIÓN SALARIAL

Tipo de Salario: [Salary Type]

Salario Diario Integrado (SDI) Anterior: [Previous SDI]

Salario Diario Integrado (SDI) Nuevo: [New SDI]

Fecha de Efectividad de la Modificación: [Effective Date]

Causa de la Modificación: [Cause of Modification]

Observaciones: [Modification Notes]

El patrón declara que el presente aviso de modificación de salario se presenta dentro del plazo legal de cinco días hábiles contados a partir de la fecha de modificación efectiva, conforme al Artículo 34 de la Ley del Seguro Social. El nuevo SDI será aplicado en el Sistema Único de Autodeterminación (SUA) a partir del bimestre correspondiente a la fecha indicada.

El nuevo SDI ha sido calculado conforme al Artículo 84 de la Ley Federal del Trabajo, integrando el salario diario base más el valor proporcional diario del aguinaldo (mínimo 15 días, Art. 87 LFT), la prima vacacional (25%, Art. 80 LFT), y demás prestaciones periódicas aplicables. Las aportaciones al INFONAVIT (5% del SDI, Art. 29 Ley del INFONAVIT) serán actualizadas automáticamente en el SUA con base en el nuevo SDI registrado.

FIRMA DEL PATRÓN

En [City], a [Notice Date].

[Employer Name]

Responsable de Nómina: [Responsible Name]

Firma: _________________________ Fecha: _________________________

Acuse de recibo IMSS Empresarial: Folio ___________________________

Fecha y hora de presentación: _________________________

Employer / Legal Representative (Patrón / Representante Legal)

________________

Signature

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What Is a IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS)?

An IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario Integrado ante el IMSS) is the official document employers use to notify the Instituto Mexicano del Seguro Social (IMSS) whenever the Salario Diario Integrado (SDI) of a registered worker changes. The notice is governed principally by Article 34 of the Ley del Seguro Social (LSS), published in the Diario Oficial de la Federación on 21 December 1995, which requires employers to communicate salary changes to the IMSS within five business days of the change taking effect.

The Salario Diario Integrado (SDI) is the comprehensive daily wage figure defined in Article 84 of the Ley Federal del Trabajo (LFT) — it integrates the base daily wage plus the proportional daily value of all recurring benefits: the aguinaldo (minimum 15 days under Article 87 LFT), the prima vacacional (25% of vacation days under Article 80 LFT), food vouchers (vales de despensa), savings fund contributions (caja de ahorro), and any other regularly granted benefits. The SDI is the sole basis for calculating IMSS bimonthly quotas (cuotas obrero-patronales) under the Ley del Seguro Social, making its accurate registration critical for both employer compliance and worker benefit protection.

IMSS quotas are calculated and remitted bimonthly through the Sistema Único de Autodeterminación (SUA) — the IMSS-mandated software that employers use to self-declare and pay social security contributions. The SUA calculates employer and worker quota shares based on the SDI recorded for each worker in the IMSS employer portal (IMSS Empresarial). When the SDI changes — due to a salary raise, a change in recurring benefits, the annual minimum wage adjustment, or a revision to the aguinaldo proportion — the employer must file an Aviso de Modificación de Salario to update the IMSS system before the next bimonthly SUA cycle.

Article 34 LSS establishes two distinct scenarios for salary modification notices. Under Article 34 Section I, when the worker has a fixed SDI (salario fijo), any change to the base salary or its component benefits requires an individual modification notice within five business days. Under Article 34 Section II, when the worker has a variable SDI (salario variable) — because commissions, production bonuses, or other variable components form part of the wage — the employer must notify the IMSS of the variable SDI update within the first five business days of each bimonthly period, based on the average daily salary earned during the preceding bimonthly period. Mixed salary structures (salario mixto) combine both fixed and variable elements, requiring modification notices for changes in the fixed component and bimonthly variable declarations.

The Comisión Nacional de los Salarios Mínimos (CONASAMI) publishes annual minimum wage increases that are effective from 1 January each year, published in the Diario Oficial de la Federación. When the CONASAMI minimum wage increase affects the calculation of the SDI — for example, because the aguinaldo proportion is calculated using the minimum wage as a reference — employers must update the SDI of all affected workers simultaneously at the start of each year. The 2025 general minimum wage is $278.80 MXN per day, and $419.88 MXN per day in the Zona Libre de la Frontera Norte (ZLFN). Failure to update SDIs following a minimum wage adjustment exposes employers to IMSS underquota assessments (diferencias de cuotas) with actualizaciones and recargos under Articles 39 and 40 LSS.

The IMSS salary modification notice also triggers corresponding adjustments in INFONAVIT contributions, since employer INFONAVIT contributions of 5% of the SDI under Article 29 of the Ley del INFONAVIT are processed through the same SUA bimonthly payment system. The Servicio de Administración Tributaria (SAT) cross-references IMSS SDI data with employer payroll ISR withholding declarations (DIOT and annual ISR return) to detect inconsistencies between reported wages and IMSS-registered salaries — a common audit trigger under the Código Fiscal de la Federación (CFF).

When Do You Need a IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS)?

An IMSS Salary Modification Notice Mexico is required whenever a change occurs in the components of a worker's Salario Diario Integrado (SDI) registered with the IMSS. Article 34 of the Ley del Seguro Social identifies the triggering events and establishes the five-business-day notification deadline that applies from the date of the wage change.

The most common trigger is a salary increase (incremento salarial) negotiated between the employer and worker — whether arising from a performance review, a collective bargaining agreement (contrato colectivo de trabajo) negotiated under the Ley Federal del Trabajo, or a unilateral employer decision to raise wages. Any upward revision to the base daily wage (salario diario base) automatically changes the SDI by increasing the proportional value of the aguinaldo and prima vacacional embedded in the SDI formula under Article 84 LFT.

The Aviso de Modificación de Salario is needed when the employer introduces or modifies recurring benefits that form part of the SDI. New or revised food voucher (vales de despensa) programmes, savings fund (caja de ahorro) contributions above the ISR-exempt threshold, transportation allowances that become habitual, or any other regular benefit granted periodically all increase the SDI and require modification notice to the IMSS. Conversely, when such benefits are legally reduced with worker agreement under Article 57 LFT, the modification notice must reflect the lower SDI.

The notice is mandatory at the beginning of each year following a CONASAMI minimum wage increase. All workers whose SDI was calculated using the minimum wage as a component — either because they earn the minimum directly or because certain benefit proportions use the minimum wage as a multiplier — require updated SDI notices filed with the IMSS within the first five business days of January.

For workers on variable or mixed salary structures under Article 34 Section II LSS, the employer must file a bimonthly salary modification notice in the first five days of each bimonthly period (January–February, March–April, May–June, July–August, September–October, November–December), reflecting the average daily variable salary earned during the preceding period. This is not optional — the bimonthly variable SDI filing is a recurring regulatory obligation tied to the SUA payment cycle.

The Aviso de Modificación de Salario is also required when an employer regularizes a previously unreported benefit — for example, when an IMSS or SAT audit reveals that commissions, production bonuses, or in-kind benefits were being paid but not included in the SDI in violation of Article 84 LFT. Voluntary correction (corrección espontánea) before an audit can reduce or eliminate fines under the Código Fiscal de la Federación (CFF) and the Ley del Seguro Social.

What to Include in Your IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS)

A valid IMSS Salary Modification Notice Mexico under Article 34 of the Ley del Seguro Social must contain the following essential elements to be accepted by the IMSS through IMSS Empresarial and to accurately update the worker's SDI for quota calculation purposes.

Employer Identification: The employer's full legal name (razón social), Registro Patronal (IMSS employer registration number), and RFC (Registro Federal de Contribuyentes assigned by the SAT). The Registro Patronal is the primary key for all IMSS modification filings and must match the record on file at the competent IMSS Subdelegación exactly. Any discrepancy triggers electronic rejection of the modification notice.

Worker Identification: The worker's full name, Número de Seguridad Social (NSS — 11 digits), CURP (18 characters), and RFC (13 characters for individuals). The NSS is the worker's permanent IMSS identifier — it remains constant across all employers and throughout the worker's entire social security history in Mexico.

Effective Date of Salary Change (Fecha de Modificación de Salario): The exact calendar date from which the new SDI takes effect. IMSS quotas are recalculated from this date. The five-business-day filing deadline under Article 34 LSS runs from this effective date. Employers should ensure the effective date documented in the payroll system, the Recibo de Nómina (pay slip) issued under Article 804 LFT, and the IMSS modification notice are identical — discrepancies create audit exposure.

Previous SDI (Salario Diario Integrado Anterior): The SDI figure currently registered with the IMSS before the modification. This figure provides the baseline for IMSS auditors to verify that quota calculations for prior bimonthly periods were correct and to confirm the change is a legitimate revision rather than a retroactive correction of a previously underpaid SDI.

New SDI (Salario Diario Integrado Nuevo): The revised SDI calculated under Article 84 of the Ley Federal del Trabajo, incorporating the updated base daily wage and revised proportional values of all recurring benefits — aguinaldo (minimum 15 days per Article 87 LFT), prima vacacional (25% of vacation days per Article 80 LFT), despensa, caja de ahorro, and any other periodic benefit. For variable SDI workers under Article 34 Section II LSS, the new SDI is the average daily salary for the preceding bimonthly period.

Salary Type (Tipo de Salario): Specification of whether the SDI is fixed (salario fijo), variable (salario variable), or mixed (salario mixto) under the framework of Article 34 LSS. This classification determines whether a modification triggers a one-time notice or a recurring bimonthly filing obligation. Workers on mixed salary must have both components — fixed and variable — separately identified.

Cause of Modification (Causa de Modificación): The reason for the salary change, such as: salary increase (incremento salarial), minimum wage adjustment (ajuste por salario mínimo), new benefit added (prestación adicional), benefit modification (modificación de prestaciones), regularization of previously unreported component (regularización), or other. This narrative supports the audit trail and demonstrates that the employer proactively identified and corrected the SDI.

Forms-legal.com provides this IMSS Salary Modification Notice Mexico template as a practical administrative guide. IMSS quota calculations involve complex actuarial tables, risk class adjustments under the Ley del Seguro Social, and coordinated INFONAVIT and SAT obligations — employers should engage a licensed contador público (CPA) or gestor IMSS to manage modification filings and SUA reconciliations. The IMSS Departamento de Auditoría a Patrones conducts employer audits that specifically examine SDI accuracy across bimonthly periods, and unexplained SDI discrepancies are a primary audit trigger.

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Forms Legal. (2026). IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS) (Mexico) [Legal document template]. Forms Legal. https://forms-legal.com/mexico/employment/forms/imss-salary-modification-notice-mexico

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BibTeX
@misc{formslegal-imss-salary-modification-notice-mexico,
  author       = {{Forms Legal}},
  title        = {IMSS Salary Modification Notice Mexico (Aviso de Modificación de Salario ante el IMSS) (Mexico)},
  year         = {2026},
  howpublished = {\url{https://forms-legal.com/mexico/employment/forms/imss-salary-modification-notice-mexico}},
  note         = {Free legal document template}
}

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