Can they require you to work more than 40 hrs a week or 8 hrs a shift?
Yes, sort of. In my contract:
If you are full time, they can insist you stay an hour over your shift. Or, it is considered job abandonment if management wants to be nasty about it. They have to let us know an hour before our shift ends tho. Your contract may differ.
Part timers have unavailable hours. Sometimes, I ask my part timers stay an hour past their shift. Some are not able to stay over so I don't enforce it. Babysitter, school or carpool.
I dont mind the OT personally. HOWEVER...If ive got plans that day (enjoyment for me) then that takes priority. I let them know ahead of time im unable to stay over due to unchangable plans.