Is it permissible, in Islamic law, to work overtime and earn money from it, knowing that government employment regulations prohibit such a thing?

The default rule is that it is impermissible for a teacher to undertake additional work that is prohibited by labor law, because the basic principle is fulfilling contracts and adhering to laws that do not contradict Islamic Sharia. However, a teacher is permitted to undertake additional work if it is with the permission of the authorized officials granted by the government, and if the work does not harm the governmental work, or if the prohibition from work is an act of obstinacy, and not for a valid reason or a recognized public interest.