All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
It is not permissible for your brother to ask for that money from the contractors that he brings to his company, and what he takes from them is a forbidden bribe.
If those tasks that he is doing are not part of his duties, then he may abstain from doing them or ask his employer (company) to pay him a fee for doing them.
However, agreeing with the contractors on a commission that they pay him in exchange for contracting them or for helping them to get these contracts is not permissible because it is a way of softening the hearts and constitutes favoritism at work.
Imaam Al-Bukhari titled a Chapter: “The person who does not accept a gift for a reason, and ‘Umar ibn ‘Abd Al-‘Azeez said, 'At the time of the Messenger a gift was a gift, and today it is a bribe.'”
A hadeeth reads, “The gifts to public servants are ghulool (unlawful earnings).” [Ahmad]
So your brother should fear Allaah and stop doing that. The solution is as we have mentioned earlier; he either refuses to do this task that is not part of his duties, or he accepts to do it and asks for a fee from his employer in return for doing it, or he accepts to do it voluntarily without expecting any compensation for it.
Allaah knows best.