The union that represents 12,000 Twin Cities nurses said Monday that it will limit any potential strike to one day, removing at least for now the specter of an open-ended walkout.

It's the latest twist in heated contract negotiations between the Minnesota Nurses Association and 14 hospitals ahead of a strike authorization vote Wednesday.

The union said a strike, if members OK it, would be only one day to limit disruptions to patient care, minimize lost income for nurses and yet still create significant headaches for hospital management.

For one thing, the hospitals could still face stiff bills for temporary replacement nurses who charge by the week.

"This will put pressure on them economically and let them know we're serious," said Joni Ketter, director of organizing and field operations for the MNA. "Our main goal is to get a good contract."

With the two sides locked in the most contentious bargaining since a five-week walkout in 1984, the nurses will vote Wednesday whether to accept the hospitals' offer or strike for one day.

Which day hasn't been determined, but MNA spokesman John Nemo said it would likely be soon after the contract expires May 31. He said nurses in other parts of the country have held successful one-day strikes.

The nurses say hospitals want to cut pension and health benefits and change work rules in ways that would endanger patients.

They also want the hospitals to commit to staffing ratios to ensure there are enough nurses to care for patients.

The hospitals say they're responding to tough economic times -- a recession and now health reform -- and that they need more flexibility to move patients around, not strict ratios.

Both sides say they remain far apart, and bargaining teams for the nurses are recommending a "no" vote on the hospitals' offer. If indeed there is a one-day strike and both sides go back to the table, the nurses would have to vote again on any new offer.

With a possible strike looming, the hospitals plan to hire replacement workers if necessary. A California agency is recruiting nurses for a potential strike in Minnesota at up to $4,770 a week, three times the average pay of a full-time hospital nurse.

"The problem for hospitals," Nemo said, "is they still have to pay replacement workers for five or seven days" since the replacements are hired in weeklong stretches.

In response, the hospitals said they remain committed to reaching an agreement before the contract expires.

"We have no interest in a strike," hospital spokeswoman Anna Youngerman said. "It's disappointing that the nurses' union is making plans for a strike when there is still time to reach an agreement."

The MNA is also accusing the hospitals of colluding in the contract negotiations.

Late Monday, the nurses association filed unfair labor practice charges with the National Labor Relations Board against the six hospital groups involved, saying they had "violated [their] obligation to negotiate in good faith by engaging in unlawful collusion."

The hospitals responded that coordinated bargaining is "nothing new."

"Just as the union is engaging in coordinated bargaining at the six tables, the hospitals are also engaged in their legal right to conduct coordinated bargaining for the contracts," Youngerman said. "The union was advised before negotiations began that these negotiations would be coordinated, as they had been in previous contract discussions."

One outside observer noted that the timing of the NLRB filing is not coincidental.

In an unfair labor practice strike, employers cannot permanently replace workers, as they could if it were a so-called economic strike, said Mark Mathison, who leads the labor practice team at law firm Gray Plant Mooty in Minneapolis. Mathison, who typically represents employers, is not involved in the current negotiations.

"At a minimum," Mathison said filing charges "would give some amount of comfort to nurses who vote to strike that they can't be permanently replaced."

Chen May Yee • 612-673-7434