Yes. In your state (this does not remain true in all states) if your pay is LOWERED, notice of a full pay period is required. Notice of a pay increase is not required. Obviously notice that your pay is remaining the same is not required.
https://www.dllr.state.md.us/labor/w...ngeofpay.shtml
So if the new pay structure results in your pay being reduced, he was required to notify you a full pay period before it went into effect.
However, let's address one other question - overtime. THERE IS NEVER, IN ANY STATE, A REQUIREMENT THAT AN EMPLOYEE BE ALLOWED TO WORK OVERTIME. It is unclear what your statement about OT, above, means. If you are working overtime and not being paid for it, that is illegal. But if you are not being allowed to work overtime, that is legal. And if your pay is reduced solely because you are no longer being allowed to work overtime, and thus not receiving overtime pay, that is not a reduction for which the state requires you be given notice.

