For months, MGB’s primary care physicians have publicly criticized their employer’s commitment to their field, the most basic kind of medical care. They have complained about pay and benefits, the size of their caseloads, the amount of support staff they get, and how much say they have over how they practice medicine. They have picketed outside Massachusetts General Hospital and Brigham and Women’s Hospital, the system’s two flagship hospitals, and in May voted overwhelmingly to unionize.

MGB, for its part, has acknowledged the discontent and in the spring vowed to make primary care a higher priority, including by investing nearly $400 million over the next five years.

In the latest development, five doctors and a nurse practitioner at an MGB practice in Medford plan to move to a Beth Israel primary care practice in the same city, more than doubling the number of providers in that office, said Sarah Finlaw, a Beth Israel spokesperson.

The Beth Israel practice is moving from 75 Riverside Ave. to a bigger location at 101 Station Landing to accommodate the new physicians. Beth Israel has been distributing fliers to patients welcoming the new providers.

All told, the MGB providers care for roughly 8,000 patients, raising the prospect that now, when those patients need to see specialists, many will go to Beth Israel instead of MGB.

MGB confirmed the impending departures Wednesday and said it will be closing the office at 137 Main St. in Medford. It said the health system has an internal medicine practice nearby and will consolidate operations. MGB said it employs about 650 primary care providers in Massachusetts and New Hampshire.

Although the departing doctors represent “a small number of our total [primary care providers] across the system, we recognize the inconvenience this may cause our patients and are committed to supporting our patients and staff through this transition,” MGB said.

A view of Beth Israel Deaconess Medical Center in Boston in 2020.David L. Ryan/Globe Staff

Patients will have the option of moving with their providers to the Beth Israel practice, seeing MGB doctors online, or transferring to another MGB practice, the health system said — although 15,000 patients in the system already have no primary care providers and have to wait months, if not longer, to see doctors in person.

MGB and Beth Israel have been competing for market share for years. The rivalry intensified in 2023 when Beth Israel lured away Brigham’s longtime partner, Dana-Farber Cancer Institute, with a promise to build a $1.7 billion, 300-bed freestanding inpatient cancer hospital in Boston’s Longwood Medical Area. MGB is fighting back by creating what it calls the Mass General Brigham Cancer Institute, a venture in which the health system is investing $400 million.

Far from the world of architectural blueprints, Beth Israel has been luring away primary care physicians from MGB, seizing on the unhappiness that doctors have publicly expressed on a variety of matters, including pay.

The typical salary of a full-time primary care doctor at MGB is about $260,000, which is also the national median, a physician active in the new union of primary care doctors recently said. The typical salary of a primary care physician at Beth Israel wasn’t immediately available.

Almost exactly a year ago, MGB officials confirmed that nine primary care doctors from a single Brigham and Women’s Hospital practice in Chestnut Hill planned to resign in February 2025 to join a new practice in Wellesley affiliated with Beth Israel. And in the summer, Beth Israel hired three MGB primary care doctors in Foxborough to join a Beth Israel practice in Canton.

All told, the 18 providers who have switched from MGB to Beth Israel, or plan to do so, care for tens of thousands of patients.

Dr. Kevin Tabb, chief executive of Beth Israel, touted his system’s hiring spree at a Massachusetts Health Policy Commission hearing this month, saying that Beth Israel has grown primary care by 30 percent over the past three years.

“I don’t think there’s another system in the state that has done that, and we intend to further grow it,” said Tabb.

MGB has acknowledged that some of its primary care doctors feel burned out and overworked. In May, MGB’s chief executive, Dr. Anne Klibanski, pledged to invest nearly $400 million to “elevate primary care,” including by hiring 90 new support staffers and by adding doctors.

MGB said Wednesday it has hired at least 114 primary care physicians since 2023. The system declined to say how many physicians have left, but doctors report that unhappy colleagues have departed to practice concierge medicine, retired, or cut their hours.

MGB also recently announced the appointment of its first-ever chief of primary care, Dr. Kimberly DeRoche, who will join the health system in February.

The 18 departures will cost MGB millions of dollars in lost revenue because of a ripple effect, according to Levy, the former head of Beth Israel Deaconess. Primary care doctors refer patients to the hospital to see specialists and undergo a broad range of procedures, from colonoscopies to heart surgeries — and all that treatment will likely shift from MGB to Beth Israel, he said.

“Most people don’t switch primary care doctors when they don’t have to, so when your primary care doctor switches to another hospital, you switch to another hospital,” said Levy, who is serving as interim chief executive of SSTAR, an addiction treatment and health center in Fall River.

The move of the six clinicians in Medford is the latest sign of discontent among primary care providers at MGB, Massachusetts’ biggest employer, with roughly 82,000 employees.

Primary care doctors at MGB voted 183 to 26 in May to join the Doctors Council of the Service Employees International Union. It was the first time that primary care physicians in Massachusetts had voted to form their own bargaining unit. The health system is challenging the make-up of the union before the National Labor Relations Board.

Primary care doctors from Brigham and Women’s Hospital and Massachusetts General Hospital picketed in December 2024.David L. Ryan/Globe Staff

Primary care doctors have criticized MGB’s leadership over a number of initiatives, including the system’s introduction in September of an artificial intelligence app to help address a critical shortage of such providers.

Called “Care Connect,” the platform was launched for the 15,000 MGB patients without a primary care doctor. A chatbot that is available 24/7 interviews the patient, then sets up a telehealth appointment with a physician in as little as half an hour. MGB is among the first health care systems nationally to roll out the app.

Several primary care doctors at MGB, however, described AI as a distraction from what they contend is the real solution to the shortage: providing the pay and working conditions that will attract more primary care physicians and keep them from leaving.

“The goal should be to retain the physicians we have,” said Dr. Zoe Tseng, a primary care doctor at Brigham for the past 11 years. Tseng said she and her colleagues want more say over their work conditions, higher pay, and better benefits, such as sick pay.

Although the shortage of primary care physicians is a nationwide problem, it’s particularly acute in Massachusetts.

More patients are reporting difficulty finding doctors. Physicians are struggling with overwhelming workloads. The corps of primary care providers is aging, and the medical education system isn’t producing enough doctors to replace them.

Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.