Short answer. For the employer, on the first day of operation. Article 170 provides that compulsory coverage takes effect on the first day of his operation for the employer, and on the date of his employment for each employee — so your business's coverage began the day it opened.
What the law says
Compulsory coverage of the employer during the effectivity of this Title shall take effect on the first day of his operation, and that of the employee, on the date of his employment.
Labor Code, Article 170 — When Coverage Takes Effect. Read the full provision →
Two separate effective dates in one rule
Article 170 fixes the effective date for coverage in a single sentence, but it actually names two different starting points: compulsory coverage of the employer during the effectivity of this Title shall take effect on the first day of his operation, and that of the employee, on the date of his employment. The employer's coverage and each employee's coverage are not tied to the same trigger — the article deliberately separates them.
The employer's coverage starts with operation, not paperwork
For the employer, the trigger is the first day of his operation — meaning the day the business actually begins operating, not the date any registration or filing was completed. A company that opened its doors and began doing business is covered from that operational start date, regardless of when any administrative step happened to be finished, or when the registration paperwork with the relevant office was actually completed.
Each employee has their own coverage clock
For an employee, the article sets a separate trigger: on the date of his employment. This means coverage does not start for every worker on the same calendar day the business opened — each employee's coverage instead runs from the specific date that individual employee began working, which will differ from one hire to the next as your workforce grows over time.
What this means for your newly opened business
Applying both parts together: your company's own compulsory coverage as an employer took effect on the first day it began operating, while each individual employee's coverage began, separately, on that employee's own date of employment. A worker hired weeks after opening day is covered from their own start date, not from the day the business first opened, and not from any later date the employer might have gotten around to formally reporting that hire.
Why the two triggers are kept separate
Tying employer coverage to the start of operations, rather than to when the first employee is hired, closes a gap that would otherwise exist between opening for business and taking on staff. Tying employee coverage to each worker's own hiring date, rather than to the employer's coverage start, means a worker is never left uncovered simply because they joined the business well after it first opened its doors.