[drcube]

There are plenty of jobs where you're technically always on call. Firefighters, paramedics, doctors, soldiers, etc. What stops employers from simply informing their employees that, from now on, they are all on call 24 hours a day?

[Argorak]

Be aware that the employers themselves are making those rules. The idea actually comes from car manufacturers in Germany.

Also, all the jobs you mentioned have contractual clauses regulating that, like payment for emergency work and payment for on-call duty.