After a one-day strike failed to nudge hospitals toward a better offer, Twin Cities nurses are poised to vote on an open-ended walkout that would significantly ratchet up the stakes for both sides.

About 12,000 nurses will vote Monday on whether to walk indefinitely. If at least 66 percent vote yes, they would need to give the hospitals a minimum of 10 days' notice but could strike anytime after that.

There have been no new dates set for negotiations.

"This is what our nurse leadership feels needs to be done," said John Nemo, a spokesman for the Minnesota Nurses Association (MNA). "The hospitals forced us to a one-day strike. We did that. The hospitals say nothing's changed. We feel they are forcing us to an open-ended strike."

The prospect of an open-ended strike had already ignited a debate on the MNA's Facebook page late Monday. One post called for nurses to "march on," while another cautioned against becoming "sheep to be led to the slaughter."

In the previous strike vote, over 90 percent of nurses voted to reject the hospitals' offer and to strike for a day. The strike happened Thursday, forcing the hospitals to fly in 2,800 replacements to keep their facilities open.

About 200 nurses still have not been called back to work at Abbott Northwestern Hospital in Minneapolis and United Hospital and Children's Hospital in St. Paul, according to the MNA. The union calls the situation an illegal lockout, while hospitals say they are calling nurses back according to patient volumes.

The MNA will meet with members on Wednesday, Thursday and Friday to explain its strategy. The vote will happen Monday at two as yet undisclosed locations, one in the west and one in the east metro.

The hospitals questioned the union's motivation.

"For the union to put forth a vote to strike indicates the union is not interested in negotiations but in conflict," said Maureen Schriner, a spokeswoman for the hospitals. "The hospitals see this as clearly driven by a national nurses union with an aggressive strategy."

The MNA is part of National Nurses United, which formed in late 2009 and has 155,000 members.

The union is pushing for nurse staffing ratios, saying that nurses are stretched so thin that patients are in danger. In addition, the union wants pay raises of 3.5 to 4 percent in each of three years.

The hospitals have refused to discuss staffing ratios, saying they need flexibility to move nurses where they're needed. They've also proposed cuts in nurses' pension and health benefits, along with raises of 0, 1 and 2 percent.

"The union must really think they made some significant progress with the public and also with their own membership," said Mark Mathison, a labor attorney at Minneapolis law firm Gray Plant Mooty.

But the vote is also a risk for the union, he said: "If the vote is against an open-ended strike, that puts the union in a bad position."

As with last Thursday's 24-hour strike, the nurses are calling this an unfair labor practice strike.

That may be one way to "assuage nurses' fears about an open-ended strike," Mathison said. If the National Labor Relations Board agrees with the union's assertion that the hospitals engaged in unfair labor practices, then the nurses can't be permanently replaced.

But until and unless the NLRB rules, "no one will know if it actually is," he said. "The more charges they file the better their odds that it would convert this from an economic strike to an unfair labor practice strike."

Nemo said the MNA filed multiple charges alleging "illegal, intimidating and/or threatening behavior by employers."