The first nurses’ strike to hit a Boston hospital in 31 years became a lockout Thursday when Tufts Medical Center refused to let the 1,200 members of the Massachusetts Nurses Association return to work until Monday.
Union members and hospital management said they plan to be back at the negotiating table sometime after Monday, but no date had been set.
The hospital and the union had tried unsuccessfully since April 2016 to agree on a new contract. On Thursday, the two sides continued to disagree, this time about the impact the work stoppage is having on patient care at the hospital, which has hired 325 replacement nurses as a stopgap.
When the union members’ 24-hour strike ended at 7 a.m. Thursday, about 100 of them tried to return to work but were turned away by the hospital’s security chief, who said they could not enter the hospital until Monday.
Moments later, union representatives each waved a hand in the air and told nurses to “start walking.”
The hospital had notified the nurses beforehand that a strike would lead to a four-day lockout.
Mary Havlicek Cornacchia, a Tufts nurse on the negotiating team for the union, known by the acronym MNA, said union nurses planned to picket outside the main entrance of the medical center 24 hours a day, most during their regularly scheduled shifts, until they are let back in.
“If you’re scheduled to work, you’re scheduled to walk,” she said of the nurses’ picketing shifts.
Family and community members returned Thursday to rejoin the nurses and continue picketing with them. Some people picketed while friends or family received treatment inside.
Cornacchia said staff nurses are concerned that their replacements are not qualified to handle the complex medical care that they regularly provide and are unfamiliar with Tufts’ equipment.
“Now they’re insisting that we stay out here and they keep their substandard nursing care that they hired and paid millions of dollars for inside,’’ she said. “We want to go back to work. We are worried about our patients.”
Speaking separately to reporters in the hospital atrium, chief nursing officer Therese Hudson-Jinks said the transition between union nurses and their short-term replacements went smoothly, and she rejected the claims that patient care has been compromised.
“It’s not uncommon when we on-board people that they need to review things,’’ Hudson-Jinks said.
But officials from the state departments of Public Health and Mental Health, which are monitoring the situation, were investigating complaints from two people, according to a spokeswoman.
Some minor issues also had arisen but were quickly corrected, according to Ann Scales, spokeswoman for the Department of Public Health, who did not specify the nature of the complaints or issues.
Matthew Larkin, vice president of operations for Tufts, told reporters the hospital has maintained its patient load, conducting more than 50 surgeries Thursday and providing treatments for roughly 300 patients in need.
Larkin said the hospital called patients in advance of the strike, informing them of what they could expect, and none canceled. “We had a very steady day yesterday,” he said.
Hudson-Jinks said management has made its best and final offer to the union.
“In the event the MNA wants to call and accept our best and final offer, yes, we would reach an agreement,” Hudson-Jinks said. “We put our heart and soul in all these negotiations.”
Cornacchia said an immediate resumption of contract talks was unlikely.
“We want to go back to work. This is not a stunt. We want to take care of our patients. That’s what this is about,’’ she said. But “right now the emotions are pretty high, so it’s probably not a good idea for either side to sit at the same table at the moment.”
The hospital said it was required to hire replacement nurses for five days and had already notified the union that if its members went on strike, the hospital would use the replacements until Monday. Hudson-Jinks said staffing levels during the lockout will match staffing levels during normal operations.
Thirteen staff nurses crossed the picket line Wednesday and reported for their regular work shifts, according to the hospital.
Both sides anticipate tension when union nurses reclaim their posts Monday.
“We know it’s going to be a different day for us,” Hudson-Jinks said. “It’s going to be unlike a day we’ve ever had. So was [Wednesday].”
The strike came after about 15 months of talks failed to produce a new contract for nurses at Tufts, a 415-bed teaching hospital that treats children and adults. The union says it is seeking increases in pay and staffing levels, but both sides are deadlocked over another key issue: retirement benefits.
The hospital wants nurses who still have pensions to move into defined-contribution plans, similar to 401(k)s, that would save the hospital money. The union has fought to keep the nurses’ pensions.John R. Ellement and Emily Sweeney of the Globe staff contributed to this report.
Sara Salinas can be reached
at firstname.lastname@example.org. Follow her on Twitter at @saracsalinas.