Is it permissible for a Muslim to report his employer who evades paying zakat, knowing that advising him could lead to significant harm to him?

If you are unable to offer advice to someone for fear of harm, you are excused. However, reporting him to the legitimate authority to exact the due right from him is considered changing an evil (munkar) and is obligatory according to one's ability, and it is also advice to the Muslim. The Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he cannot, then with his tongue; if he cannot, then with his heart—and that is the weakest of faith." And due to his saying, peace and blessings be upon him: "Religion is advice."