Are the salaries of employees in a company that manufactures paper, and whose capital is a joint venture between usurious banks, insurance companies, and a national company, considered part of the forbidden usurious return?

If the majority of a company's capital is unlawful (haram), then working for it is prohibited. However, if the majority is lawful, it is preferable to avoid working there, as it is considered disliked (makrooh), and some scholars have deemed it prohibited. The unlawfulness of earnings is not due to the return being usurious (riba-based), but rather due to the prohibition of dealing with someone whose wealth is predominantly unlawful.