Thousands of nurses at five Minnesota hospitals went on strike Monday in a dispute over health insurance, workplace safety and staffing levels. Here's a look at some of the issues:

Which hospitals are involved?

They're all part of Minneapolis-based Allina Health — Abbott Northwestern and the Phillips Eye Institute in Minneapolis, United in St. Paul, Unity in Fridley and Mercy in Coon Rapids. About 4,800 nurses at those hospitals are represented by the Minnesota Nurses Association, the union that called the open-ended strike.

What's the main dispute?

Health insurance.

In a move Allina estimates would save $10 million a year, it wanted to switch nurses from their union-only health plans to ones that cover all other Allina employees, meaning nurses would pay lower premiums but have higher deductibles and out-of-pocket expenses.

That mirrors a national trend toward shifting costs on to employees with higher deductibles and patients picking up more out-of-pocket costs. The union has resisted, saying nurses are more prone to injuries and illnesses because of the hazards of their jobs.

Allina has since altered its position, offering to let the nurses keep their two most popular plans. But the union says that's a step backward because Allina would pick up only 2 percent of whatever cost increases the plans incur (the company later offered to increase the cap to 3 percent and delay implementing the cap until 2019). The union also says the plans eventually would become so expensive that the nurses would have to drop out and the plans would die.

How will a strike affect patient care?

Allina officials say it won't and didn't in June when nurses at the five hospitals walked out for a week. The union disputes that. The hospitals have been lining up replacement nurses, but that's an expensive proposition. Bringing in 1,400 replacement workers from across the country was a major reason why June's strike cost $20.4 million, Allina acknowledged in a recent financial disclosure statement. The union says Allina has been pressuring nurses to cross the picket lines and keep working.

What's the status of negotiations?

The two sides met Friday with federal mediators. The 22-hour talks broke off early Saturday with no agreement on a new three-year contract, and no new talks scheduled. The contract expired June 1.

How long could a strike last?

Hard to say. Union leaders have said nurses will stay off the job for as long as it takes. The June walkout was only scheduled to last a week.

The last big open-ended nurses' strikes in the Twin Cities lasted 23 days in 2001 and 38 days in 1984.