TB testing required by law for HCWs?

My hospital routinely gives PPDs to all Hospital staff annually. I had a doctor question this and the only thing I can come up with is that OSHA's position that employers shall offer the TB skin tests. It is not mandatory for the employee to participate, only that the employers make TB testing available to the employees. We're in IL.
I had always thought this was mandated by one of the regulatory agencies. Any comments on this would be appreciated!