Nurses at Tufts Medical Center in Boston are planning to go on a one-day strike on July 12, while the hospital has hired enough replacement nurses for a five-day lockout.

The Massachusetts Nurses Association gave the hospital the required 10-day notice of the strike action on July 1 after the union rejected what Tufts called its final offer last month.

“We do not want to strike,” Mary Havlicek Cornacchia, an OR nurse and MNA’s bargaining unit co-chair, said in a statement, “but management has left us with no other choice. They won't hear us. They don't believe us when we say that the contract improvements we are fighting for are necessary in order to keep patients safe, and in order to keep Tufts Medical Center competitive in a city full of top-notch hospitals. We want to be inside on July 12 caring for our patients, but if striking is the only way to get management to hear us and to take our issues seriously then we will be on the streets instead.”

The union listed among its priorities: improved nurse staffing with safer assignments and additional IV and clinical resource nurses. It said Tufts has operated with “constant unsafe staffing levels” with registered nurses temporarily reassigned or asked to pick up shifts in a “disjointed and superficial” attempt to address staffing challenges.

The hospital’s leaders have focused on disagreements over changing a defined-benefit pension plan they say covers only one-third of Tufts nurses. According to the Boston Business Journal, its last offer was a 10.5 percent wage increase for most of the hospital’s nurses along with increased staffing in exchange for the concession on the pension plan.

“The defined benefit plan covers fewer than one-third of our 1,200 nurses and seven percent of our 5,000 employees,” said Tufts’ chief nursing officer Terry Hudson-Jinks, MSN, RN. “Six million dollars a year is wasted on administrative costs to run the plan; this is money that does not go to our nurses. At a time when hospitals are being asked to be more responsible with our patients’ health care dollars, continuing this plan is irresponsible.”

Boston Business Journal had previously reported the union was seeking to strike on a date “most harmful to the hospital (from an economic standpoint)” and members had suggested walking out after interns began working in July.

While the nurses’ union had planned on a one-day strike ending at 7 a.m. on July 13, Tufts said any striking nurses won’t be allowed to return to work for five days. The $5 million cost of bringing in replacement nurses will come out of its proposed wage increases for nurses. The union said if the hospital moves ahead with the lockout, nurses will stay on the picket line.

The two sides are scheduled to meet along with a federal mediator for the 35^th time just before the one-day walkout. A last-minute agreement was able to avert the last planned strike by the MNA at Brigham and Women’s Hospital in 2016.