what would you do if an employee threatens to quit if you do not double her hours?
There is a couple of possible solutions to this problem. Firstly, as a manager, you should explain an employee that there are certain job safety requirements in place, so the company has to comply with these requirements. In case there is a possibility of adding extra hours (not doubling them) to the existing schedule, you should use it to reach consensus. Secondly, you can explain to the employee that he\she will work less productively with extra hours appointed.