IMSS Employee Deregistration Form Mexico (Baja de Trabajador ante el IMSS)

An IMSS Employee Deregistration Form Mexico (Aviso de Baja de Trabajador ante el IMSS) is the official document used by Mexican employers to notify the Instituto Mexicano del Seguro Social (IMSS) that a worker's employment relationship has ended and that social security contributions must cease. The form is governed principally by Article 15, Fraction I of the Ley del Seguro Social (LSS), published in the Diario Oficial de la Federación on 21 December 1995, which imposes on every employer the mandatory obligation to register and deregister workers with the IMSS within the legally prescribed deadlines.

The Aviso de Baja is not merely an administrative courtesy — it is a legal obligation with direct financial and penal consequences. Under Article 304-A of the Ley del Seguro Social, employers who fail to file the baja within five business days of the termination date are subject to monetary fines calculated on multiples of the Unidad de Medida y Actualización (UMA), the reference unit established by the Ley para Determinar el Valor de la Unidad de Medida y Actualización published in the DOF on 30 December 2015 to replace the minimum wage as the index for social security and fiscal penalties. Continued IMSS contribution charges accrue until the baja is properly registered, exposing the employer to both actualizaciones (inflation adjustments) and recargos (surcharges) on unpaid quotas under Articles 39 and 40 LSS.

The IMSS operates through a digital portal system known as IMSS Empresarial, which replaced the earlier IDSE (IMSS Desde Su Empresa) platform. Employers file the Aviso de Baja electronically through IMSS Empresarial using the empresa's Registro Patronal (employer registration number) issued by the IMSS upon the initial Alta Patronal (employer registration). The Sistema Único de Autodeterminación (SUA) — the software platform used to calculate bimonthly IMSS quotas — automatically adjusts contribution calculations once the baja is processed. Each worker is identified in the IMSS system by their Número de Seguridad Social (NSS), a unique 11-digit identifier assigned upon first registration, and their CURP (Clave Única de Registro de Población), the 18-character national identity code issued by the Registro Nacional de Población (RENAPO).

The Aviso de Baja triggers several downstream administrative actions within the IMSS system. The worker's access to IMSS healthcare services (Seguro de Enfermedades y Maternidad) continues for a grace period of eight weeks following the baja under Article 109 of the Ley del Seguro Social — a protection designed to ensure workers are not left without medical coverage immediately upon termination. The worker's AFORE (Administrador de Fondos para el Retiro) retirement account under the SAR (Sistema de Ahorro para el Retiro) overseen by the Comisión Nacional del Sistema de Ahorro para el Retiro (CONSAR) is not closed upon baja — accumulated retirement savings remain in the worker's individual account for future recovery or transfer to a new employer's AFORE registration.

IMSS deregistration also affects the INFONAVIT housing fund. When the IMSS baja is processed, INFONAVIT contributions automatically cease through the coordinated system between IMSS and the Instituto del Fondo Nacional de la Vivienda para los Trabajadores (INFONAVIT), since INFONAVIT contributions are calculated and remitted through the same SUA bimonthly process as IMSS quotas. Workers with active INFONAVIT credits (créditos INFONAVIT) who are deregistered must review their credit status with INFONAVIT directly, as ongoing credit repayment obligations may transition from payroll deduction to direct payment.

The Secretaría del Trabajo y Previsión Social (STPS) through its Inspección del Trabajo division and the IMSS through its own inspection units (Subdelegaciones IMSS) have authority to audit employers for compliance with baja filing timelines. Under Article 251 of the Ley del Seguro Social, the IMSS has broad inspection powers to demand production of employment records, IMSS baja receipts (acuses de recibo), and payroll documentation for any audited period. The employer must retain IMSS baja receipts for at least five years as part of the obligatory accounting and payroll documentation requirements under Article 804 of the Ley Federal del Trabajo (LFT) and Article 30 of the Código Fiscal de la Federación (CFF).

An IMSS Employee Deregistration Form Mexico is required whenever an employment relationship ends, regardless of the reason for termination. Article 15, Fraction I of the Ley del Seguro Social creates an unconditional obligation for the employer to file the Aviso de Baja within five business days of the date the employment relationship concludes — failure to comply within this window constitutes a regulatory infraction that triggers automatic IMSS fines and continued quota accrual.

The baja is required upon voluntary resignation (renuncia voluntaria) by the worker under Article 50 of the Ley Federal del Trabajo. Even when the worker provides adequate advance notice and both parties agree to an orderly departure, the employer's IMSS deregistration obligation does not depend on the completion of any settlement or finiquito payment — it runs from the last actual working day. Filing the baja early (before the termination date) is equally prohibited, as IMSS considers premature deregistration an attempt to evade quota obligations during active employment.

The Aviso de Baja is mandatory upon justified dismissal (rescisión justificada por causa imputable al trabajador) under Article 47 of the Ley Federal del Trabajo. The employer who rescind the employment relationship must simultaneously notify the Centro Federal de Conciliación y Registro Laboral (CFCRL) and, within five days, file the IMSS baja. Where the worker contests the dismissal before the Tribunal Laboral, the IMSS baja does not suspend the legal proceedings — the employment status before the IMSS and the pending labour dispute are treated as separate matters.

The form is needed when an employment contract reaches its natural end — for fixed-term contracts (contratos por tiempo determinado) under Article 37 LFT, specific-work contracts (contratos para obra determinada) under Article 36 LFT, or seasonal contracts (contratos de temporada) under Article 39 LFT. At the expiry of each such contract, the employer must file a baja even if the worker will be rehired immediately for a new contractual period — in practice, employers file baja and alta in quick succession for recurring seasonal arrangements.

The Aviso de Baja is also required when a worker dies during employment. The employer must notify the IMSS of the death and file the baja, which triggers the IMSS pension survivor benefit (pensión de viudez, orfandad, y ascendencia) evaluation process for the deceased worker's dependents under Articles 64 through 70 of the Ley del Seguro Social. Simultaneously, the employer must process the finiquito payable to the estate and notify INFONAVIT of the death to initiate any applicable life insurance coverage under the INFONAVIT credit terms.

Under Article 304-B LSS, employers who submit false information in IMSS baja filings — such as backdating the termination date to avoid quota obligations — face criminal liability in addition to administrative fines, with potential prosecution under the Código Penal Federal for tax fraud offences. The IMSS maintains a digital audit trail through IMSS Empresarial that timestamps all submissions, making retroactive manipulation detectable during IMSS subdelegación inspections.

A valid IMSS Employee Deregistration Form Mexico under Article 15 of the Ley del Seguro Social must contain the following essential elements to be accepted by the IMSS and to protect the employer from continued quota obligations and regulatory sanctions.

Employer Identification: The full legal name (razón social) or name of the employer (patrón) together with the Registro Patronal (employer IMSS registration number) assigned upon the Alta Patronal. The Registro Patronal is the primary identifier for all IMSS transactions and is formatted as a letter followed by ten or eleven digits, corresponding to the employer's registered class and geographic subdelegación. The employer's RFC (Registro Federal de Contribuyentes) assigned by the Servicio de Administración Tributaria (SAT) must also be included for cross-referencing with SAT payroll records.

Worker Identification: The worker's full legal name (nombre completo), NSS (Número de Seguridad Social — 11 digits), CURP (Clave Única de Registro de Población — 18 alphanumeric characters), and RFC (13 characters for individuals) must all be recorded accurately. Any discrepancy between the name on the IMSS baja and the IMSS system records will cause rejection of the electronic filing and require manual correction through the IMSS Subdelegación — a process that can cause delays and continued quota accrual.

Termination Date (Fecha de Baja): The exact calendar date on which the employment relationship ended. This is the critical figure that determines the cut-off date for IMSS quota calculation. The date must match the termination date documented in the finiquito or settlement agreement (convenio de terminación laboral) and, where applicable, the date recorded in the CFCRL conciliation record. Filing with an incorrect termination date — particularly a date earlier than the actual last working day — constitutes a violation of Article 15 LSS and triggers IMSS surcharges on the underpaid quotas.

Cause of Termination (Causa de Baja): The IMSS baja form requires selection of one of the standardized cause codes established by IMSS regulations: voluntary resignation (renuncia voluntaria), justified dismissal (rescisión patronal justificada), unjustified dismissal (rescisión patronal injustificada), contract expiry (término de contrato), death (defunción), permanent disability (incapacidad permanente), or other specified causes. The cause code affects downstream IMSS benefit eligibility calculations for the worker, including whether pension-qualifying service periods are credited.

Registered Daily Salary (Salario Diario Registrado ante el IMSS): The Salario Diario Integrado (SDI) that was registered with the IMSS for IMSS quota calculation purposes must be confirmed on the baja form. This figure — calculated under Article 84 of the Ley Federal del Trabajo to include base daily wage plus the proportional value of aguinaldo, prima vacacional, and other recurring benefits — must match the SDI on file with the IMSS. Any SDI correction should be processed through a separate salary modification notice (Aviso de Modificación de Salario) before or simultaneously with the baja.

IMSS Subdelegación: The territorial IMSS administrative office (Subdelegación) with jurisdiction over the employer's registered workplace. Mexico is divided into IMSS delegaciones and subdelegaciones by geographic zone, and the baja must be processed through the competent subdelegación. Electronic filings through IMSS Empresarial are automatically routed to the correct subdelegación based on the employer's Registro Patronal.

Electronic Filing Receipt (Acuse de Recibo Electrónico): The IMSS Empresarial platform generates an electronic receipt (acuse de recibo) upon successful baja submission, displaying the folio number, submission timestamp, and confirmation of accepted data. This acuse de recibo is the legal proof that the employer complied with the Article 15 LSS deadline — employers must print and retain this document as part of their IMSS compliance file for at least five years.

Forms-legal.com provides this IMSS Employee Deregistration Form Mexico template as a practical guide for documenting the baja process. Every IMSS transaction involves regulatory risks that require review by a licensed contador público (CPA) or abogado laboralista with IMSS compliance expertise. Employers with significant workforces should engage an IMSS-certified specialist (gestor IMSS) to manage electronic filings and audit readiness, given that IMSS inspection visits (visitas de inspección) are routine and carry substantial fine exposure under Articles 304-A and 304-B of the Ley del Seguro Social.