Is the money that engineers take from the subcontractor as a "brokerage fee" permissible or impermissible, with the knowledge of the employer?

If recruiting contractors is part of the engineers' work in a contracting company, then it is not permissible for them to take a commission from them without the employer's knowledge. This is because an employee is not allowed to take compensation for work for which he already receives a salary, or to perform unauthorized work during his working hours. Furthermore, taking a commission is suspect of favoritism, collusion, and overlooking work, thus it would be considered bribery. Therefore, it is not permissible for them to accept it without the employer's permission.