If we give an employee a "perk" upon being hired of say, a free safety deposit box, do we have to provide them with a 30-day notice that we will begin charging a safe deposit box fee once they have left our employ?

I believe that we communicate all changes at the time of Exit. For example, we give our employees the "best" checking account type we have, but charge no fees. At the time of Exit we would offer them the option to change to a free account or keep the same account type, now with a fee.

To avoid dealing with the question of whether the employee left voluntarily or if you terminated them, you could make it a standard procedure that effective with the next statement cycle, annual renewal, etc., they will be charged a fee to continue the checking account or safe deposit rental.

If you followed the requirements of Reg DD, you could disclose up front that an event such as leaving the bank's employ, will trigger a change. §230.5, OSC (a)(1)3

The safest thing to do is to remind them and make new disclosures though I don't think that has to be an absolute requirement.