Is the financial amount an employee receives as a personal commission, without the client's knowledge, considered unlawful, given that the administration approves of it and the employee receives a basic salary for his work, and would his pilgrimage be accepted if he intended to perform Hajj with this money?

For the commission to be permissible, the company's management must authorize it, and it should not be part of the agreed-upon salary to avoid ambiguity. It is not a condition for the client to know that the commission is specifically for you, as long as they are aware of the total amount for the service. However, increasing the fee for the client without their knowledge is forbidden and considered deception and treachery. Performing Hajj with money acquired in this manner is not permissible. The money must be returned to its rightful owners, or if that is not possible, it should be given as charity.