So today on my supervisor's desk I saw a note with PS 2574 (resgination) and an arrow pointing to my name. I'm recently converted and on probation. Is there anything that can be done if they try to get me to sign it? Will the union fight for me? I'm a good employee, very rarely late, I've called in only once last week due to a legitimate emergency and I called a different supervisor a head of time to make sure it wouldn't affect me. I always do what I'm told, never talk back. Sure I've made mistakes, but I correct them and move forward. I've been at this office just under 2 years and about 3.5 years with the post office in total.

I'm already not going to sign if it comes to it, but will I be able to keep my job?

Edit: I forgot to mention I'm a clerk.