https://blogs.scientificamerican.com/observations/why-would-hospitals-forbid-physicians-and-nurses-from-wearing-masks/

Health care workers across the country are battling against COVID-19 with dwindling access to personal protective equipment (PPE), including masks. For hospitals reaching crisis capacity, the CDC has recommended that nonrespirator masks (surgical or procedural) be worn during select procedures and prolonged contact with potentially infectious patients. But guidance for health care workers on wearing these masks in other common areas of the hospital—outside of a patient room—is not well-developed.

As a result, some health care workers are facing the threat of disciplinary action for wearing masks in the hallways, elevators and shared clinical and nonclinical areas of hospitals—in some instances even if they come from the worker’s own supply.