Health insurance coverage was cut off Friday for thousands of Montefiore nurses as the largest nurses strike in New York City entered its fourth week.

Picketers continued to brave the cold Sunday at the Montefiore Einstein campus in Morris Park. More than a week ago, Montefiore warned nurses that if they did not return to work by Feb. 1, they would forfeit their health insurance coverage. Sunday marked that deadline, and nurses on the picket line said they have no intention of returning until their demands are met.

The strike began 21 days ago after the New York State Nurses Association called on hospitals to address safe staffing levels, improve health benefits and take steps to prevent workplace violence. After weeks of negotiations, the union says no agreement has been reached.

As some hospitals increase pay for travel nurses to address staffing shortages during the strike, union nurses say they remain firm in their demands for contract improvements.

“We need safe staffing,” said Anne Farrington, a Montefiore nurse of 15 years. “In the emergency room, patients are packed together. It’s not dignified. We need better care for our patients.”

Nurses are expected to return to the bargaining table Saturday.