Union nurses raised the stakes another notch in their dispute with Twin Cities hospitals on Friday, saying they will strike July 6 if contract talks fail to produce a settlement by then.

Unlike their 24-hour walkout June 10, this would be an open-ended strike, with the prospect of millions of dollars in losses to both sides and the potential for serious disruptions to Twin Cities health care.

Meeting reporters the morning after a day of contract talks, union leaders expressed frustration with the pace of negotiations.

"We felt we've been at this for three months, and we haven't settled anything,'' said Cindy Olson, a critical-care nurse at St. John's Hospital in Maplewood and a negotiator for the Minnesota Nurses Association.

Negotiators for both sides agreed not to discuss specifics from Thursday's talks, but Olson said that the day was a "disappointment'' and that talks would not resume until Tuesday afternoon.

A spokeswoman for the hospitals was quick to agree, but she pointedly blamed the nurses.

"In the three months that we've been negotiating, we've gone from an itemized list of about 33 items we wanted to negotiate, and we're down to about 12," said Maureen Schriner. "Where is the union? Despite their assurances that they're willing to modify or delete any proposal, they haven't changed a single one of their proposals since we started."

Experts watching the dispute say it's hard to say whether the July 6 deadline makes a strike more likely or is designed to produce a settlement.

"It seems like the union is trying to accelerate the negotiations,'' said Aaron Sojourner, an assistant professor at the Carlson School of Management at the University of Minnesota. The union seems to be saying that "we're tired of this dragging out and we want to have serious negotiations.''

At the same time, he added: "It's very hard to read these kinds of situations because [it's] like they're playing chicken.''

John Remington, another University of Minnesota labor scholar, pointed out that the law requires a 10-day notice in health care strikes and that it could serve as a cooling-off period. "But it may also be the union's message that we're serious -- we want to expedite this, and if that doesn't happen, we're prepared to strike,'' Remington said.

Both sides said they continue to hope for a negotiated settlement, but they agreed on little else.

Olson said that the union had been prepared to continue negotiations all night Thursday and continue Friday but that the hospitals declined.

Schriner said it was the federal mediator who proposed resuming the talks Tuesday, suggesting both sides try to find areas in which they can modify their positions. "The union says there should be a big rush,'' Schriner said, "but the only rush we see is a monumental rush toward a strike. What's the point in meeting if they won't negotiate?"

The nurses' one-day strike this month led the hospitals to hire nearly 3,000 temporary replacements and postpone hundreds of elective procedures but appeared to cause only modest disruptions to patient care. A longer strike would impose much greater costs on both sides, cause wider disruptions to the health care system and raise the prospect of hospitals considering permanent replacements.

"The alternative [to a negotiated settlement] is ... to bring in permanently many thousands of new nurses to run the hospitals [and] for these thousands of nurses to find new jobs,'' Sojourner said. "The two sides need each other, long term.''

The affected hospitals are: Abbott Northwestern, Mercy, Unity, United and Phillips Eye Institute (all owned by Allina Hospitals and Clinics); St. John's, St. Joseph's and Bethesda (owned by HealthEast Care System); North Memorial; Children's Hospitals and Clinics of Minnesota; Park Nicollet Methodist; Fairview Southdale and the Riverside campus of University of Minnesota Medical Center, Fairview.