A long-brewing union effort at Massachusetts General Brigham hospitals moved forward this week after a majority of the hospital’s medical residents, interns, fellows and other trainees signed cards indicating their support for a union. The hospital declined to voluntarily recognize the union on Monday.

For workers, the next step is a formal election overseen by the National Labor Relations Board, something employees hope to hold by the end of April.

If successful, the state’s largest health care system would join a wave of unionization at hospitals across the country. The union effort at Mass General Brigham began at the start of the pandemic, growing as pressure mounted on frontline workers, including trainees who were often pushed into different roles.

“During COVID, people were pulled off of electives to work in the hospital,” said Dr. Sascha Murillo, a third-year internal medicine resident at Massachusetts General Hospital. “Things that were kind of career-defining were put on hold so that we could take care of patients in the hospital due to COVID.”

Pandemic burnout was a major factor in the decision to move forward with a union, according to Dr. Kayty Himmelstein, a fifth-year infectious disease fellow at both Massachusetts General Hospital and Brigham and Women’s.

“It was really scary and dramatic, but it was also something we were really proud to be able to do,” Himmelstein said. “All we really wanted was for our work to be respected, for our employer to compensate us fairly and to have concern for our safety and the well-being of our patients. Unfortunately, while all of our frontline providers were really doing our best to care for our neighbors, we didn’t really feel like our employer had our back.”

In deciding not the voluntarily recognize the union, Mass General Brigham cited “the unreliability of union cards as an indication of employee support due to the fact that peer pressure is so often a factor,” according to a statement from Mass General Brigham’s interim chief academic officer Paul Anderson.

The union effort seeks representation from the Committee of Interns and Residents, a local branch of the Service Employees International Union, for more than 2,500 employees in residencies, fellowships and training programs at Mass General Brigham hospitals including Massachusetts General Hospital, Mass Eye and Ear, Brigham and Women’s Hospital, Newton-Wellesley Hospital, Salem Hospital and Spaulding Rehabilitation Center.

Himmelstein said residents regularly work 80-hour weeks and 24-hour shifts while struggling to make ends meet.

“People are living paycheck to paycheck. They’re rationing food at the end of the month. They’re turning down the heat,” she said. “What we’re looking for is compensation that would allow folks to meet their basic needs, live close to the hospitals and continue to focus on our patients.”

Grueling schedules take a toll on the health of medical residents, Himmelstein said, which trickles down to patients.

“When we’re working 80 hours and sometimes more a week, we’re often not able to access routine primary care, dental cleanings, prenatal appointments and other things we need to do to take care of ourselves,” she said. “When we’re not able to care for ourselves, when we’re worried about our own survival, we’re not able to bring the best of ourselves to our patients.”

Residents say they have been called into meetings with their supervisors to discuss the union effort, and multiple emails have been sent out to staff with information regarding the union. “If there were ever a time to not sign a card, that time is now,” an email from last month reads. The risk of unionizing, hospital representatives wrote, would mean that “your entire relationship with Mass General Brigham — including program and education leadership — would change, and in many ways you might not like.”

Trainees who begin their first year of residency this summer will earn a salary of $78,540, according to Mass General Brigham’s salary scale. Last month, hospital officials announced a 10% salary increase for all residents and clinical fellows, a $10,000 annual stipend, and increases in health insurance benefits, according to a statement from a hospital spokesperson. Health insurance has been offered at no cost to all residents since last year, and that benefit will be extended to fellows starting in July, at the onset of staff turnover.

The hospital says the wage and benefit increases were not related to union activity, but part of a “multi-year process” to adjust compensation and benefits, according to a web page created by the hospital to answer questions about the union effort.

“Mass General Brigham has always been and remains committed to providing very competitive and attractive wages and benefits to our Trainees,” the website reads. “Our residents and clinical fellows are integral to patient care and represent our next generation of physicians.”

These changes have been requested for years, Himmelstein said.

“We’ve been describing how we’re struggling to afford to live in Boston and we haven’t really received much of a response, and so we’re really glad that our organizing effort has achieved this response,” she said. “We want to make sure that we defend it, and that it’s written into our contracts so that we can continue to advocate and so that our future colleagues who come after us will be able to advocate for the resources they need.”