Register the obra with IMSS and check REPSE before subcontracting

Put the SIROC registration on the mobilisation checklist alongside the hoarding and the site office, with an owner and a date. It carries the type of work, where it is and the tasks that will be carried out, and it is due within five working days of the works starting, under article 12 of the Reglamento del Seguro Social Obligatorio para los Trabajadores de la Construccion por Obra o Tiempo Determinado. Keep the reference against the project once it is filed.

Яагаад: Five working days is roughly the time it takes to get the site fenced, so this obligation competes with everything else in the noisiest week of the job and loses. It is also the record every later IMSS question is answered from: without an obra registered, the contributions your workers generate have no work to attach to, and reconciling them afterwards is a task nobody has budgeted.

Record attendance by day and by worker, and keep your own employees separate from the people a subcontractor brought. Do it as part of the daily routine rather than as a monthly reconstruction, because the value of the record is that it was written on the day.

Яагаад: The line between your workforce and somebody else's is the line the whole subcontracting reform turns on, and it is drawn on site rather than in the contract. A specialist whose people take their instructions from your foreman, use your tools and appear on your attendance list is not providing a specialised service whatever the contract says, and that is precisely how an inspection reads it.

Run the payroll from the attendance rather than beside it, so the workers paid, the workers registered with IMSS and the workers on site are the same list. Keep the contributions attributable to this obra visible against the project, because that is the form the IMSS question takes.

Яагаад: Three lists that should be identical are maintained by three different people, and nothing compares them until somebody outside the firm does. The gap is rarely fraud; it is a worker who started on Monday and was registered on Thursday, repeated across a year. Reconciled monthly it is a small correction, reconciled at an inspection it is an assessment.

Check two things in the STPS register and file the evidence with the date you checked it: that the provider holds a current REPSE, and that the activity it is registered for actually covers the work you are asking for. Then check the other half, which is your own: that the work is a specialised service or work outside your corporate purpose and predominant economic activity, rather than the placing of people at your disposal, which is prohibited.

Яагаад: A payment to a provider that should have been registered and was not is not deductible for ISR, and the IVA on it is not creditable, so the cost of the mistake is the subcontract value plus the tax that was supposed to come back. The registration also has a term and can be lost, so a REPSE verified once at engagement is not evidence of anything two years later, and the verification has to carry a date to be worth filing.

Give notice of the subcontract to IMSS within five working days of the day it was signed, using the format the system requires, and log the submission and its acknowledgement against the project alongside every other filing to an authority. The count runs from signature, not from the day the subcontractor first turns up.

Яагаад: Signature and mobilisation can be weeks apart, and the deadline attaches to the earlier of them, so a subcontract signed in good time and started later is already late before anybody has done anything wrong. Logging the acknowledgement matters as much as filing: an obligation you believe you met is worth nothing at an inspection without the receipt.

Make the monthly pack a condition of payment rather than a request: the REPSE still current, the opinion del cumplimiento de obligaciones fiscales, evidence that the IMSS and housing fund contributions for the period were paid, and the CFDI de nomina of the people who did the work. Release the payment against the pack, not against the promise of it.

Яагаад: This is the only leverage that exists. Once the money has gone the documents arrive slowly or not at all, and the exposure is yours rather than theirs, because it is your deduction that fails and, where a subcontractor does not pay its workers' contributions, your works those workers were on. A pack that is a condition of payment arrives every month without anybody chasing it.

File the closure of the works in SIROC when they finish, and archive the labour compliance pack with the rest of the close-out documents: the registration and its amendments, the subcontract notices, the monthly evidence and the payroll reconciliations, kept together and kept for as long as the tax and social security records have to be kept.

Яагаад: An obra left open goes on looking like a live site to IMSS long after the hoarding came down, and it is the finished jobs that get audited, because the people who ran them have moved on and the folders have been split between offices. Archived as one pack at the close, the answer to an inspection two years later is one folder rather than a fortnight.