All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Contracts and transactions have been legislated to facilitate for people and meet their needs. One of these is Ijarah contract (a contract for hiring of services of a person for a specified period in exchange for a specified consideration). From the perspective of Sharia, the transaction referred to in the above question is framed as Ijarah.
In such contract, it is conditioned that the benefit is specified and has a value, and the wage is specified as well. It is stated in the Shafie book [Moghni Al-Mohtaaj, vol.6, pp.130]: "In order for the Ijarah contract to be valid, it is conditioned that the benefit is specified, has a value and lawful."
According to the above question, this is classified as Ijarah Fi Ad-Dhimmah (Fair wage). The company hires the medical center, including doctors and equipment, to provide medical care to its staff members. Moreover, it isn`t conditioned that the medical center provides its services to the staff of this company only. Rather, it is hired to provide its services to others as well. Imam An-Nawawi says: "In Ijarat Al Dhimma, the hired person-tailor, goldsmith and the like-provides services to different people and organizations. However, the person or establishment hired to provide services to a particular party only and for a particular period isn`t permitted to serve other parties during that same period. [Rawdat At-Talibin, vol.5, pp.228].
The margin of Gharar (uncertainty) involved in such contracts is excusable since it is inconsiderable in such general needs. Imam An-Nawawi said: "In principle, any sale contract involving Gharar is invalid….This refers to apparent Gharar that can be avoided. However, the sale contract in which Gharar can`t be avoided-house foundations-is valid according to scholarly consensus." [Al-Majmou`, vol.9, pp.258].
In conclusion, it is permissible for the above medical center to receive a certain sum of money in exchange for providing medical care services to company staff contracting with it and this form is framed as Ijarah in return for a known wage. And Allah The Almighty Knows Best.