That is false as i work for a union with GM and in the rules states only 5 hours minium needed between shifts. It is not illegal for them to work you more than 8-10 hours a day. Thats why theres overtime which they must pay due to labor laws. but if you dont work past a full time(40+) week overtime isnt added to the paycheck.
Right now im working 32 hours a week. Which is full time so if i work say 40 i still get paid normal rate. If i do say 41 hours that one hour is over time.
Just keep in mind if you work say 2 16 hour shifts they by law dont have to give you over time till your OVER 40.