Is it permissible for the husband to force his wife to quit her job, given their difficult financial situation, and threaten her with divorce, especially since the husband is not religious?

If you fear that your livelihood will be lost by leaving your job and that your husband cannot cover the household expenses in his current situation, then strive to convince him that your work is to assist him. If he insists, then involve relatives to speak with him. If he persists in his stance, you have the choice between taking the matter to court or refusing to leave your job until he provides for your maintenance. However, if he is providing your due maintenance, but it is not as expansive as you desire, and he orders you to leave your job, then you must obey him. We advise you to counsel him and remind him of Allah at the appropriate time with gentle words, and to pray for his well-being, righteousness, and guidance.