As an MHA for almost a year now this is a HUGE word of advice:

Paper trail, paper trail PAPER TRAIL.

Listen, some of these supers (especially at the plant I work at) will try and scare you out of your job. I've dealt with it so many times. And because I'm apart of the Mail Handlers union I have written many of statements.

It may not be a grievance but there's at least a paper trail. That includes all my call ins and all accomodations from doctors. These supers will not take you by your word (unless you got a cool super that will but 99.9% will not).

Start up a paper trail and get that going. Because if for any reason they bring you into the office (make sure you have representation with you) you can legit say hey, I've got this paper trail and all this documentation so I don't know why you're writing me up for whatever reason when I've clearly shown xyz.

Don't let them scare you outta your position, even if you are a MHA, PSE, etc. the only difference between y'all and the regulars is that y'all are temporary and don't have a full time position. They all started where you are, don't let them treat you any differently, ESPECIALLY supers.

Start that paper trail now, you'll thank me later.