Company is strong arming recruiting companies from hiring people with their certifications.

I've been working at a large HealthCare organization (we'll call it organization X) that's in the process of implementing a new electronic medical records system. This company has hired me as an at will employee and paid my training and certification of the third party medical records system they are using. Many people have used their experience from this project to obtain better paying positions at other healthcare organizations using the same third party vendor, however I have been told that recruiters are now no longer "allowed" to hire people from organization X because the third party vendor has now deemed our certification non-transferrable. This is neither stated or implied in any documentation. This new policy was put into effect by the medical records system vendor supposedly because they wanted to ensure more successful implementations of their product, however what this does for the people that hold this certification is that it renders them unmarketable outside the organization where they got their certification. They've artificially controlled the market for people that are certified in their product. This drives down the wages for these employees because other employers are no longer competing for these people. Is this legal?