All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Companies whose primary activity is permissible, but engage in forbidden activities such as usurious loans and the like, are permissible to work in, as long as the employee does not engage in the forbidden activities.
In that case, it is not considered as assisting in what is forbidden.
However, if the employee in these companies engages in forbidden transactions in his work or is assigned to them, then it is not permissible to work in them, except in cases of necessity where the employee cannot meet his essential expenses from another permissible source.
Allah knows best.