Two pediatricians at Cleveland's University Hospitals used an internal physician directory to contact colleagues about forming a union. In response, they say that UH disciplined them for trying to unionize. They've filed unfair labor practice charges with the NLRB.
Section 7 of the National Labor Relations Act protects employees' rights to engage in concerted activity—including organizing a union and discussing it with co-workers. That protection applies whether you're a warehouse worker or a pediatric subspecialist.