Is it permissible, Islamically, for the sponsor to prevent the worker from another job opportunity, or to control his future, or to deport him, knowing that the worker has paid for his residency expenses and procedures, and the salary he receives is very low?

The sponsorship system (kafala) has two aspects: The first: an attachment contract, which involves forbidden, unjust practices. The second: a lease (ijara) as a contract of exchange. The worker commits to its conditions after concluding the lease contract with the sponsor (kafeel). He has the right to demand a salary increase or a transfer of sponsorship (naql kafala) and termination of the contract. If the sponsor agrees, then that is well and good; otherwise, the worker must be patient until his contract expires. The sponsor has the right to deport the sponsored person (makfool) if the contract period ends and the sponsor has fully paid the worker's dues.