My previous place of employment was a poster brat for why unions are necessary. They manufactured a lame excuse to fire me just so they could steal my accumulated vacation and sick leave.
That is what state Labor Boards are for.
They can “steal” your accumulated sick leave, but they cannot steal any accrued vacation. They either have to let you take the time or pay you for it at your current hourly rate upon termination. That is Federal law (ERISA) and is not subject to modification by any state. If they didn’t pay you for accrued vacation upon termination, you have grounds for a federal lawsuit.