I have no problem with that, as long as you pay for what is worth.
I know engineers who had work where their had to be on call like that. However they were doing rotation and they were being compensate for all the time they had to be on call.
From what I remember they were getting 0.3 days of paid holidays for each 12h they were being on call. This was on top of their 5 weeks+ of paid holidays (France).
I think the issue is not the work ethic of the employees, but the ethics of the employer in this case.
Edit: I forgot to say but if course if they are actually called then they get paid for the hours they spend at the factory on top of the compensation.