Yes, that’s an excellent question.
If the government employee’s contract included this compensation, then I think it should be honoured. However, if it wasn’t included in the contract, then I don’t know if the government has any obligation to pay it. That said, I think the current budget grandfathers the payments.
I’m also not sure if government positions necessarily pay less than private industry positions. Based on the links which I posted in an earlier message, I don’t think this assumption is accurate.