Years ago I got a weekend job that was every other weekend and filling in if people had to call out. I did this because at the same time I worked multiple per diem jobs during the week.
During the week there were normal day shifts, and then an evening shift that was only from 6-8pm. I was the only person on my team that didn't live within walking distance so to all of them doing that shift was not a huge deal. I lived a 15 minute drive away. I also don't drive due to a vision impairment so it was both not worth my time to go to this shift, but also a waste of time for whoever had to drive me there.
The issue here was that one lady had to stop doing those shifts for a while and I filled in thinking my boss would find someone new to take them over permanently. She didn't so I started to complain because this was interfering with all of my other jobs. Some were understanding and would let me leave early. Some were not and I would have to forgo an entire actual shift of money for a 2 hour shift only that day. (if anyone is interested in knowing what I did at the time I will comment it so it makes sense why I couldn't work partial shifts at other jobs sometimes)
Also, at this time I was taking pottery classes/working at that shop and the owner ended up going through major cancer treatments. They were going to lose the shop basically because they didn't have the energy or time to run it how it needed to be run, so the final straw was when I put my foot down at my job because I was taking on teaching pottery classes and running their shops most nights (that didn't interfere with my every other weekend) to keep the pottery shop open.
My boss got HR and other administrators involved in my case asking if my “other obligations” would take me away from my job there and really prying into business that wasn't theirs. I made it quite clear that I would be working what I was obligated to work and that nothing would be interfering with that. But any shifts outside of that would have to work around my schedule.