Had a job where my hours were Monday-Friday. No weekends, except on volunteer basis.
One Friday after we'd had a bad snowstorm, my boss asks if I want to come in Saturday to help catch up on the work. That weekend happened to be my birthday and I had plans, which I mentioned, and I declined the weekend work.
Cue to later that evening as I'm punching out and a different manager says "Hey I'll see you tomorrow thanks for helping out with the delayed deliveries" and I say "I told Joe Schmoe that I couldn't work, I have plans" and this guy says "Well we have you down to work, if you don't show up it'll be a no-call;no-show and you'll be written up"
I didn't go into work that weekend.
Monday morning I get called into the supervisors office and they're telling me they gotta write me up, and I told them it's bullshit and why and walked out.
The thing about working today especially hourly paid jobs is how little voce employees have now. it's all rigged to favor the employer. If you told them you couldn't work, it should have ended there since you said weekends were volunteer basis but I guess they just ignored that and that sort of stuff is why some workers need unions.