Hilchos Lashon Hara, chapter 1, section 6

Even if he sees that not speaking negatively against a Jew or other forbidden speech will cause a great loss in his livelihood, nonetheless, he many not speak lashon hara. For example, if the people employing him lack fear of heaven and will fire him if he is not a baal lashon hara as they are, and through this he will have no livelihood for his household, nonetheless, it is forbidden just like all other negative commands where one is obligated to give all he has in order not to transgress them.