Salary Increase Letter Mexico (Carta de Aumento de Salario)

A Salary Increase Letter Mexico (Carta de Aumento de Salario or Carta de Incremento Salarial) is a formal written notification issued by a patron (employer) to a trabajador (worker) documenting a permanent upward revision of the worker's base salary (salario base), specifying the new daily, biweekly, or monthly wage and the effective date of the increase. The letter creates a binding modification to the employment contract under the Ley Federal del Trabajo (LFT) — published in the Diario Oficial de la Federación on 1 April 1970 and reformed through 2022 — and triggers mandatory updates to the worker's Salario Diario Integrado (SDI) registered with the Instituto Mexicano del Seguro Social (IMSS) and reported to the Servicio de Administración Tributaria (SAT) through the CFDI de Nómina (payroll tax receipt) system.

The foundational legal basis for salary determination in Mexico is Article 86 of the Ley Federal del Trabajo, which establishes the equal pay principle (a trabajo igual, salario igual): equal work performed under equal conditions, same shift, and same employer must be remunerated with equal pay regardless of the worker's sex or nationality. The Carta de Aumento de Salario must comply with this principle — salary increases cannot be applied discriminatorily or used to create disparate compensation among workers performing equal functions. Article 3 LFT reinforces this by prohibiting wage discrimination on grounds of sex, age, disability, social condition, religion, migration status, ethnic origin, or sexual orientation.

Salary increases must always respect the Salario Mínimo General (SMG) established annually by the Comisión Nacional de los Salarios Mínimos (CONASAMI) under Article 90 LFT. For 2025, the general minimum wage is $278.80 MXN per day in the general zone and $419.88 MXN per day in the Zona Libre de la Frontera Norte (ZLFN) — the northern border free zone. No employment contract may stipulate a salary below the applicable minimum wage, and any increase that brings a salary above the previous minimum must be reflected in an updated IMSS SDI modification filing (aviso de modificación salarial) within five business days of the effective date of the increase under Article 34 of the Ley del Seguro Social (LSS, published in the DOF on 21 December 1995).

The salary increase also triggers a recalculation of the Salario Diario Integrado (SDI) under Article 84 LFT. The SDI incorporates the new base daily wage plus the proportional daily values of all recurring benefits: the aguinaldo (minimum 15 days under Article 87 LFT), prima vacacional (25% of vacation days under Article 80 LFT), and any other periodic benefits. An increase in base salary therefore automatically increases the SDI and the corresponding IMSS bimonthly quotas (cuotas obrero-patronales) calculated on the SDI and remitted through the Sistema Único de Autodeterminación (SUA).

For INFONAVIT purposes, the employer must also report the new SDI to INFONAVIT under Article 29 of the Ley del INFONAVIT, as the housing fund contribution of 5% of the SDI increases proportionally with the salary increase. The Sistema de Ahorro para el Retiro (SAR/AFORE) managed by CONSAR records the updated contributions in the worker's individual retirement account (subcuenta de vivienda), directly affecting the worker's INFONAVIT credit scoring and retirement savings accumulation.

For ISR withholding purposes, the employer must adjust the monthly ISR withholding calculation under Articles 94 and 96 of the Ley del Impuesto sobre la Renta (LISR, published in the DOF on 11 December 2013) to reflect the new salary. The CFDI de Nómina issued from the effective date of the increase must reflect the new compensation — any CFDI de Nómina that underreports the actual salary triggers SAT penalties under the Código Fiscal de la Federación (CFF). The SAT cross-references CFDI de Nómina data with IMSS SDI records through the Programa de Fiscalización Integrada, so both registries must be updated simultaneously.

The Carta de Aumento de Salario also serves as the formal amendment to the employment contract under Article 57 LFT, which provides that contract conditions may be revised by mutual agreement between the parties. Any revision that reduces the worker's previously established salary is null and void under Article 5 LFT — only upward modifications are lawful without the worker's explicit written consent reviewed and approved before the Centro Federal de Conciliación y Registro Laboral (CFCRL).

A Salary Increase Letter Mexico is needed whenever an employer grants a permanent upward revision of a worker's base salary or integrated daily wage, regardless of the reason for the increase.

The letter is most commonly needed following annual salary reviews. Most medium and large Mexican companies — operating as Sociedades Anónimas de Capital Variable (SA de CV) or Sociedades de Responsabilidad Limitada (S de RL) — conduct annual performance reviews and general salary adjustments (revisión salarial anual) during the first quarter of each calendar year. The Carta de Aumento formalizes the outcome of these reviews and creates the written record required by Article 804 LFT for the employer's personnel file (expediente laboral). In unionized workplaces governed by a contrato colectivo de trabajo (CCT), salary revisions are typically negotiated with the sindicato and formalized through a convenio de revisión salarial deposited with the Centro Federal de Conciliación y Registro Laboral (CFCRL) under the 2019 reforma laboral — but individual workers not covered by the CCT or workers receiving superior benefits (prestaciones superiores a la ley) still require a personal Carta de Aumento.

The document is needed when CONASAMI announces the annual minimum wage increase. Each year, typically effective 1 January, the Comisión Nacional de los Salarios Mínimos publishes the new Salario Mínimo General under Article 90 LFT. Employers must issue salary increase letters to any worker whose current salary falls below the new minimum or who must receive a proportional adjustment to maintain internal pay equity. Failure to pay the new minimum wage is a violation of Article 90 LFT and exposes employers to fines under Articles 992 through 1002 LFT and IMSS underreporting sanctions under Article 304-A LSS.

The Carta de Aumento is also needed when a worker receives a merit increase (aumento por mérito), a productivity bonus restructured as a base salary component, or a cost-of-living adjustment (ajuste por inflación). Each of these changes requires a formal written notification to comply with the employer's documentation obligations under Article 25 LFT (which lists minimum contractual terms to be documented in writing) and to support the updated IMSS SDI modification filing (aviso de modificación salarial) required within five business days of the effective date under Article 34 LSS.

In restructuring scenarios — where companies merge, are acquired, or change their legal structure under the Ley General de Sociedades Mercantiles (LGSM) — workers may receive salary adjustments as part of the transition. Under Article 41 LFT, the transmission of a company through merger, acquisition, or asset transfer (substitución patronal) does not terminate the employment relationship, but any salary changes agreed as part of the transition must be documented through a Carta de Aumento or a formal employment contract amendment. The Tribunales Laborales will treat undocumented salary changes as unproven in any subsequent dispute over agreed compensation.

Finally, salary increase letters are needed for regulatory compliance. The STPS Inspección del Trabajo may request employers to produce documentation showing that workers receive compensation at or above the applicable minimum wage and that IMSS SDI modifications have been filed promptly. The Carta de Aumento, together with the IMSS aviso de modificación salarial and the updated CFDI de Nómina, constitutes the complete documentary trail required to demonstrate compliance.

A valid Salary Increase Letter Mexico under the Ley Federal del Trabajo must contain the following elements to create a binding salary modification, satisfy IMSS reporting requirements, and comply with SAT payroll documentation standards.

Issuer and Worker Identification: Full legal name (razón social) and RFC of the employer, together with the name, job title, RFC, CURP, and IMSS NSS (Número de Seguridad Social) of the worker receiving the increase. The issuer must be the employer or a person with authority to bind the company in personnel matters under Articles 11 and 12 LFT. The letter must be printed on official company letterhead (membrete oficial).

Current and New Salary: The worker's current base salary (salario base actual) and the new base salary (nuevo salario base), both expressed as a daily figure in MXN to facilitate IMSS SDI calculation. Where the salary is stated monthly or biweekly, the daily equivalent must also be computed: for a monthly salary, divide by 30.4 (average calendar days) or by the number of working days depending on the payroll structure. The percentage increase (porcentaje de incremento) is typically also stated for transparency.

Effective Date: The precise date (fecha de entrada en vigor) from which the new salary applies, expressed in DD/MM/YYYY format. The employer must file an aviso de modificación salarial with IMSS within five business days of this date under Article 34 LSS. CFDI de Nómina issued from this date must reflect the new salary. Any retroactive adjustment requires a supplementary acta de modificación retroactiva specifying the catch-up amount.

Updated SDI Calculation: The new Salario Diario Integrado (SDI) calculated under Article 84 LFT incorporating the new base daily wage plus proportional values of aguinaldo (15 days minimum divided by 365), prima vacacional (Article 80 LFT — vacation days multiplied by 0.25 prima percentage, divided by 365), and other recurring benefits. The letter or an attached calculation worksheet should show the SDI breakdown so that the worker can verify the IMSS reporting. The updated SDI must match the figure reported in the IMSS aviso de modificación salarial.

Minimum Wage Compliance Statement: An express confirmation that the new salary equals or exceeds the Salario Mínimo General established by CONASAMI applicable to the worker's work location — or the Salario Mínimo de la ZLFN if the workplace is in the Zona Libre de la Frontera Norte (municipalities including Tijuana, Mexicali, Ensenada, Nogales, Ciudad Juárez, Piedras Negras, Nuevo Laredo, Reynosa, and Matamoros). This clause demonstrates compliance with Article 90 LFT.

Equal Pay Acknowledgment: A brief clause confirming that the salary increase complies with the equal pay principle of Article 86 LFT and that the new salary is consistent with the compensation of other workers performing equivalent functions in equivalent conditions within the same establishment. This protects the employer against discrimination claims before CONAPRED and the Tribunales Laborales.

IMSS and INFONAVIT Update Notice: Confirmation that the employer will file the corresponding IMSS aviso de modificación salarial (IMSS Form AFIL-06 or equivalent through the employer's IMSS portal) within five business days of the effective date, and will update INFONAVIT contributions in the next applicable bimonthly period. Workers should verify the update by checking their IMSS account (IMSS Digital) and INFONAVIT subcuenta balance approximately 30 days after the effective date.

Signature Block: Signatures of both the employer representative and the worker acknowledging receipt (acuse de recibo) of the salary modification, date and city of signature, and the worker's RFC and CURP for identity confirmation. Article 25 LFT requires employment conditions to be documented in writing, and the worker's signature acknowledging the increase provides evidence that the modification was consensual and compliant with Article 57 LFT.

Forms-legal.com provides this Salary Increase Letter Mexico template as a practical starting point for formalizing salary revisions. Employers should ensure that IMSS SDI modification filings and SAT payroll records are updated simultaneously with the issuance of the letter to avoid regulatory penalties.