Is it legal for a public school to give an exclusive contract to a mental health agency and deny others access

I work in a school district that has an exclusive contract with a local private mental health provider. The contract allows this provider the ability to come onto any of the campuses in the school district to provide counseling and case management services to only the students who are already receiving services by the provider in the provider's clinic. Other students who are not already going to the clinic are not seen by the personnel of the provider at the school.

The problem is that there are two other mental health providers who see some of our students but they are not allowed to step into the schools during the school day, even with permission from a parent. Thus, the benefit of receiving counseling from their providers is denied by the contract.

Something about this doesn't seem right and I am hoping to find out a court case or legal statute that either supports this or doesn't. Thanks ahead of time.