My center has decided to change how they staff operations for both Black Friday and New Year's Eve. In the past all drivers were asked to volunteer and they would then force from the bottom up to ensure full staffing. This year they are forcing from the bottom up and then allowing FT drivers to volunteer as needed. I was on vacation for Black Friday but was told that only one FT driver worked. In past years it was not uncommon for as many as 10 FT drivers to work. I have told my mgt team that I would like to work New Year's Eve but have been told by all three that they would prefer to use casuals and air drivers. My question is this---if I volunteer to work and am not allowed to can I grieve this based on past practice? I am not interested in debate on whether or not I should work as that is a personal decision.