Is money taken in exchange for referring agreed-upon work to other workers permissible or forbidden?

It is permissible for someone who has been hired for a specific task to hire another to perform it, unless the employer stipulates that he must undertake the work himself. If the employer agrees to terminate the original contract, then the one who directs another worker to the task may take a fee from him for this referral (brokerage). Based on this, the lessee can hire others to do the work unless the lessor stipulates that he must undertake it himself. If such a condition is made, and both parties agree to terminate the lease, then the lessee may direct others to the work and agree with them on a specific fee or compensation in exchange for waiving his right in the contract, if they undertake to contract with the employer.