A change in pay only goes into affect from when you are told of it--of the details of the change; i.e. what your pay will be--forward. While long lead time or advance notice is not required, you must be paid as per your existing arrangement or agreement (even if only an oral one) until you get notice. You can't have the notice of the change or your wage be retroactive--you need to be told before you do the work for which you are being paid the new wage.That said, the only way to enforce your rights in this regard would be  by suing, and unless it's a very large difference, that would not be worthwhile. Once you get the new check, you'll know the wage going forward; therefore, you're talking about only being uninformed for one pay period (i.e. the first pay period that you are paid under the new structure). It is unlikely that the the difference in pay between old and new pay structure for one pay period would be worth a lawsuit.