More than 4,000 nurses at Allina Health hospitals are expected on Monday morning to take the most extreme measure they can in union contract talks: walking off the job until a deal is reached.

A lingering question is when Allina might exercise its own nuclear option — declaring a negotiating impasse.

That declaration is used sparingly in labor negotiations, especially in health care, because it signifies that both sides have reached a standstill, and it empowers the employer to simply implement its most recent contract offer. In this instance, that would allow Allina to phase out the union-backed health insurance plans that nurses have fought tenaciously to protect in talks that have dragged on since February.

“Assuming the parties have been bargaining in good faith ... the employer can say, ‘Look you guys, go ahead and strike. Fine. We’re going to impose our final offer and you can take it or leave it,’ ” said John Remington, a University of Minnesota labor relations scholar.

Allina has said that declaring an impasse is a possibility, but a spokesman said: “We’d rather continue trying to work with the union to get to an agreement our nurses support.”

Imposing contract terms can be risky, especially if it alienates a labor pool of nurses that remains in short supply and plays a key role in the functioning of any hospital.

The threat of an impasse nonetheless has been a concern for officials with the Minnesota Nurses Association (MNA), the union representing 4,800 Allina nurses at United Hospital, Mercy Hospital, Unity Hospital, Abbott Northwestern Hospital and the Phillips Eye Institute — especially now that the talks have dragged on for seven months.

“This employer has been trying to artificially create an impasse so they can either implement their terms on the nurses and/or replace the nurses,” MNA spokesman Rick Fuentes said in an e-mail.

Last-ditch talks continued for 22 hours Friday and early Saturday but failed to produce a new three-year contract, despite the involvement of a federal mediator.

Initially, Allina wanted to eliminate all four union-backed health plans — which have older, expensive benefit structures with low or no deductibles — and move nurses to its corporate insurance plans.

The two sides agreed in Friday’s talks to temporarily keep two of the union plans, but couldn’t agree on who would pay for their future cost increases and when they would be phased out as well.

The stalemate produced a seven-day strike in June, and then a vote for the second strike, which is set to start on Labor Day. In preparation, Allina recruited 1,500 temporary nurses from across the country. Half worked in the prior strike, said Allina spokesman David Kanihan.

While essential services will continue at all of the hospitals, some specialty services such as water births might be shelved. Tours and prenatal classes for expectant mothers have been canceled at Abbott.

Far apart

Nursing strikes aren’t uncommon: Kaiser Permanente in California endured a four-day strike this year, while Brigham and Women’s Hospital in Boston staved off a walkout by 3,300 nurses with a last-minute deal. But a Star Tribune review of data from the Federal Mediation and Conciliation Service shows that multiple work stoppages in the same contract dispute are infrequent.

There have been 17 instances since 2005 when hospital workers went on strike multiple times; nurses at Alta Bates Summit Medical Center in California went on strike nine separate times from 2011 through 2013 in a fight to preserve benefits for part-timers as well as sick time and education leave policies.

“The rarity of having two strikes in the same contract negotiations ... reflects how far apart the sides are,” said John Budd, a University of Minnesota industrial relations professor.

Before Allina can impose its most recent contract offer, it must satisfy a federal requirement that it first negotiate in “good faith.” The union has filed more than a dozen claims with the National Labor Relations Board (NLRB) — the arbiter of good faith in negotiations — arguing that Allina has tried to create an impasse by refusing to budge on its health insurance demands.

“The bargaining has been, basically, a pantomime,” said attorney Brendan Cummins, who filed the MNA claims.

Allina officials disagreed, noting that the offer to preserve two union health plans was a concession and that the health system met the union’s demands on workplace safety and staffing and offered $500 bonuses.

They countered that the union’s actions this summer have been part of a national, coordinated series of strikes designed to hurt hospitals by drying up the pool of replacement nurses.

“Our revised proposal is one I strongly believe our nurses would support, rather than to strike and leave the patients they serve so well,” said Dr. Penny Wheeler, Allina’s chief executive.

The good of the patient

The current negotiation is similar to 2010, when 12,000 nurses from Twin Cities hospitals struck for one day in June and then voted for an open-ended strike. A last-minute deal averted that second strike.

Remington said it would be hard to declare an impasse considering both sides offered new compromises in their most recent talks, but it could happen if the strike lingers and progress stalls. Allina officials will need to feel confident that they have negotiated fairly and that the union won’t prevail in its claims to the NLRB, he said.

“If it doesn’t appear they’ve bargained to the bitter end, the board might be inclined to view it as an unfair labor practice,” he said. “That could swing a lot of bargaining power to the union side. They don’t want it in the paper that Allina was found guilty of ... failing to bargain in good faith.”

One reason impasse declarations are uncommon in health care is that both sides feel compelled to reach agreement for the good of patients, said David Larson, a senior fellow at the Mitchell Hamline School of Law’s Dispute Resolution Institute.

“If you’re working on an assembly line and you go on strike, it might not affect your conscience that the shampoo bottles aren’t being filled,” he said. “But for many health care providers, many nurses, what brought them into this profession ... is they genuinely care about the people they are taking care of.”