Allina Health has told the union representing 4,800 nurses at its Twin Cities hospitals that they need to abandon their costly union-backed health plans, leaving nurses with an impending vote on whether to sacrifice a treasured benefit or go on strike.

Negotiations concluded early Tuesday — the final day before the current three-year contract expires — as the Twin Cities' largest health system presented the Minnesota Nurses Association (MNA) a final offer that would move the nurses to the plans its other employees receive.

The union health insurance plans "have not kept pace" with reforms in health care financing, Allina said in an online document explaining its position, "making them very expensive for Allina Health and for our nurses."

The health system says it would save $10 million by moving nurses away from the union plans, which have traditional benefit structures of higher premiums but low co-pays and deductibles and broad doctor networks. The health insurance plans for other Allina employees offer lower premiums but more cost-sharing features designed to make employees more prudent in their health care purchases, and some of them offer incentives for using Allina doctors.

Nurses believe the $10 million in savings would come at their expense, and that the union health plans are a benefit they protected while making other sacrifices in the past.

"MNA nurses have fought for decades to protect their benefits and their contract," the union said in a Monday update on negotiations. "Now Allina Health wants to take these benefits back."

The rising cost of health benefits prompted Allina to hold out while other major hospital-clinic systems in the Twin Cities reached three-year contracts with MNA nurses earlier this year that left health plans intact.

Voting on Allina's offeris scheduled for June 6, with a yes vote by nurses approving the contract and a no vote setting the stage for a strike. Any such walkout wouldn't happen immediately; the union is required to give Allina 10 days' notice first.

Nurses for Allina, Fairview, HealthEast, North Memorial, Park Nicollet and Children's hospitals conducted a one-day strike amid contract talks six years ago. Nurses with Fairview Southdale and the University of Minnesota Medical Center participated in a 23-day strike during contract talks in 2001.