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.
No one is permitted to be an employee or a manager of a company that deals in Riba (usury and interest), since he is considered a partner in such forbidden dealings. No doubt Riba is one of the greatest sins and one's earnings are not lawful, i.e. one's members of family are not allowed to use such earnings except in case of a dire need. In other words, they are permitted to take only according to their necessity. Then, they have to advise him to give up such a work, since there are so many means for earning lawful livelihood.
It is sufficient for one to know that he will face the most serious punishment in this worldly life and the Hereafter.
Allah Says (what means): {O you who have believed, fear Allaah and give up what remains [due to you] of interest, if you should be believers.) And if you do not, then be informed of a war [against you] from Allaah and His Messenger. But if you repent, you may have your principal-[thus] you do no wrong, nor are you wronged.} [Quran 2:278-279]
Allah also Says (what means): {… And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty.} [Quran 5: 2]
Thus, a good Muslim follows what Allah orders, not his own caprice. If one believes that such earnings in such a company are not lawful, this does not change the Sharee’ah ruling in this concern, i.e. Riba is forbidden.
From the Sharee’ah point of view, the company's dealing in Riba before one assumes his position does not constitute a true reason for him to continue in such a position unless he can change the policy of the company, i.e. to make them avoid dealing in Riba. In such a case, it becomes his duty to do so.
Also, governmental decisions do not change what is forbidden into something lawful, and vice versa. Furthermore, such decisions do not make dealing in Riba lawful. Only one who is forced to take usurious loans can do so, especially if he has no other source of livelihood as trade or working for government.
Allah Knows best.