The deal, struck between the union's bargaining committee and one of Mass General Brigham's two flagship hospitals, would provide Brigham's roughly 4,000 nurses with pro-rated bonuses and new guidelines governing the hospital's use of temporary nurses. It still must be approved by rank-and-file members, who rejected an earlier tentative contract forwarded by the committee last month.

"I'm incredibly proud of the Brigham nurses who stood strong to protect the world-class patient care we provide," said Kelly Morgan, union chair and a longtime labor and delivery nurse at the hospital. "We secured this agreement with the help of countless community members, patients, unions and elected officials who supported us for many months. By standing together, we protected patients and the future of union nursing care at the Brigham."

The agreement came after months of escalating pressure, including a large picket outside the hospital in July that drew thousands of nurses. The strike, had it proceeded, would have affected one of Boston's busiest and most prominent medical centers, disrupting care for patients across the region.

The tentative deal's provisions on temporary nurse staffing are likely to be closely scrutinized by members, who have raised concerns about patient safety and the erosion of permanent, unionized nursing positions. The pro-rated bonus structure also represents a compromise from earlier demands.

The ratification vote has not yet been scheduled. Union leaders said they would present the full terms to members in the coming days.

Mass General Brigham, the state's largest health care system, operates Brigham and Women's Hospital alongside Massachusetts General Hospital. The system has faced mounting labor unrest in recent years as nurses and other workers press for better pay, staffing levels and working conditions amid rising health care costs and corporate consolidation.

The Brigham deal follows a similar pattern at other institutions: earlier this week, the MIT Graduate Student Union reached a tentative agreement with university leaders, bypassing a planned strike. Those outcomes suggest a renewed willingness among employers to negotiate at the eleventh hour rather than absorb the operational and reputational costs of a work stoppage.

For patients and families in Greater Boston, the immediate crisis has been averted. But the final outcome now rests with the nurses themselves, who will decide whether the agreement goes far enough to address their concerns about staffing, safety and the future of their profession at the Brigham.