Short answer. One year. Article 290 of the Labor Code requires an unfair labor practice arising from Book V to be filed with the appropriate agency within one year from the accrual of that practice, and provides that it is otherwise forever barred. That is much shorter than the money-claim period.
What the law says
All unfair labor practice arising from Book V shall be filed with the appropriate agency within one (1) year from accrual of such unfair labor practice; otherwise, they shall be forever barred.
Labor Code, Article 290 — Prescription Of Offenses. Read the full provision →
Two clocks in a single provision
The article carries two periods, and they are easy to confuse because they sit in consecutive sentences. Offences penalised under the Code and its implementing rules prescribe in three years. Unfair labour practice arising from Book V must be brought within one year. The shorter period is the deliberate one: these disputes turn on the state of a workplace at a particular moment — who was organising, who was transferred, what was said in which meeting — and the law does not want them litigated on memories years old. Assume one year unless advised otherwise.
The year runs from accrual, not from discovery
The clock starts on the accrual of the practice, which in ordinary terms means when the act complained of occurred. Not when the union pieced together what had happened, not when the members voted to proceed, and not when the matter was endorsed to counsel. Where the conduct is a course rather than a single incident — a series of transfers, refusals or dismissals — each act carries its own accrual date, so an older incident may already be barred while a recent one is not. Fixing the date of each act is therefore the first task, not a detail.
A live money claim can create a false sense of time
This is where unions and members most often lose ground. The same set of facts frequently generates both an unfair labour practice and money claims, and money claims have three years to run. Someone checks the wage side, sees that there is time, and assumes the whole matter can wait. It cannot. The two claims prescribe on different schedules and the shorter one can expire while the other is comfortably alive. Nothing in this article suspends the one-year period while an internal grievance, a mediation or a negotiation is being pursued.
Build the chronology while it is still fresh
Because everything depends on dates, record them as the events happen rather than reconstructing them later. For each incident note the day, what was done, by whom, to whom, and who witnessed it. Keep the memos, notices, roster changes and messages in their original form, and keep the union's own records — registration papers, minutes, membership lists — since these fix when the organising began and when management can be shown to have known of it. Take that chronology to a lawyer early; a year passes faster than it sounds.