In the western region you have to inform your direct supervisor, and/or a steward within "(5) working days of the known occurrence giving rise to the dispute, alleged contractual violation or grievance."
If the matter is not settled within one day, you then file a grievence. The exception to that is underpayment on a paycheck of less than $20 for part timers. They can add that amount to your next paycheck.
That doesn't mean remedies can't stretch back further than the 5 days. Under our rider, claims for shortages on pay checks can go back 90 days. And that, still, does not prevent you from seeking remedies through state or federal law. Once you've gotten your back pay through the contractual grievance process, you can seek further remedies as allowed for through State agencies, and possibly the courts. In my state, I don't believe there is a limit on how far back you can go to claim underpayments on your paycheck. Your mileage may vary.