In this issue of JAMA, Ahmed et al 1 report that approximately 1 in 10 health care workers are union members and that union membership is associated with higher wages, better benefits, and more equitable compensation across races and ethnicities. This analysis opens a new and timely avenue of research into the impact of unionization on the health care workforce.At a time when health care workers are expressing severe levels of job dissatisfaction, there is renewed interest in the possibility that unions might offer a vehicle to address some of the most disconcerting trends in modern medicine. 2 While Ahmed et al focus on the health care workforce generally, physician unions may deserve particular consideration. Although only 6% to 8% of current physicians are union members or employed under a union contract, harnessing physician influence through unions might advance interests that extend beyond pay and benefits. They might also improve the governance of health care systems and foster the delivery of ethical, high-value medical care.Prospects for health care unions are taking shape because of the transformation of physician employment in the country. For more than a century, US physicians both enjoyed and demanded professional independence, and as recently as 2012, 60% of practices in the US were physician-owned, with only 5.6% of physicians working as direct hospital employees. The last decade, however, has seen a surge in acquisitions of physician practices, and now 52.1% of physicians are employed by hospitals or health systems, with an additional 21.8% employed by other corporate entities. 2 The large-scale employment of physicians under a single corporate umbrella is a sea change in US medicine that has not yet been fully assimilated by the profession or the health sector. Physician independence has always meant more than an economic status. It has been the foundation of a professional ethos that imbues a dedication to science, a devotion to patient welfare, and a broad commitment to the health of the public. Critically, the medical and moral authority that physicians have enjoyed, and shouldered, in blazing the scientific revolution of the past century has rested largely on professional sovereignty. 3 What happens to the medical profession and to medical practice when physicians become employees? The loss of economic independence does not necessarily mean the loss of professional independence, though it might. Such a loss would be a tragic transformation of US medicine. Unions offer an avenue through which professional sovereignty can be maintained even when physicians find themselves employed inside corporate entities.