Nurses at St. Vincent’s Hospital are set to picket outside the Greenwich Village hospital today over failing contract negotiations, a phenomenon that is playing out at several hospitals citywide.

Since December, nursing contracts at some of the city’s major academic medical centers, including Montefiore Medical Center, NewYork-Presbyterian Hospital, St. Luke’s-Roosevelt Hospital, Mount Sinai Medical Center, and St. Vincent’s, have all expired.

Against the backdrop of a nationwide nursing shortage, some negotiations are turning contentious over disagreements concerning nurse staffing levels. Last week, a group of Mount Sinai nurses picketed outside the Upper East Side hospital, and a similar scene could play out in the coming weeks at NewYork-Presbyterian’s Washington Heights campus, according to union officials at the New York State Nurses Association, which represents 35,000 nurses statewide.

“It’s just been a trend over the past several weeks here that we’ve seen with the major medical centers,” a union spokesman, Mark Genovese, said of disputes at several hospitals. Hospitals “keep trying to cut corners, and they’re trying to force their existing staff to do more with less,” he said.

At St. Vincent’s, which emerged from bankruptcy last year, a federal mediator has been called in to moderate negotiations set for Friday. In addition to staffing levels, the nurses oppose a practice of temporarily assigning a nurse to a unit, or “floating,” which they say compromises patient safety.

“We’re pretty far apart right now,” a member of the union’s negotiating team, John Hiltunen, said. “If some progress isn’t made, we would have to take a strike vote.”

Mr. Hiltunen, who has worked at St. Vincent’s for 17 years, said that in 2005, when the hospital sought bankruptcy protection, the hospital’s 1,200 nurses forfeited a raise “to help the hospital in a trying time.” Now, they seek to “make up in negotiations what we lost last time,” he said. The base salary for nurses at St. Vincent’s is $63,990 annually.

In a statement, the hospital acknowledged the “superb, compassionate care” its nurses provide, and said it intended to negotiate with them “at the bargaining table to reach an equitable agreement.”

A major sticking point for the Mount Sinai nurses is a proposal by the hospital to restructure their time off. The union, which represents 1,900 Mount Sinai nurses, said the proposal would require nurses who are sick to miss eight days of work if they want to claim “sick days.”

The hospital dismissed that notion, and said in a statement that the union’s “assertions are inaccurate.”

“In fact, the Hospital has not proposed any reduction in sick time but has proposed a more flexible way for nurses to use their benefit time, which could provide a majority of the nurses with even more scheduled time off,” the statement read.

While contract negotiations are rarely smooth, this year’s disputes are playing out against the backdrop of a well-documented nursing shortage, which has compounded the usual squabbling over nurse-to-patient ratios, salary, and benefits.

In 2006, the federal Health Resources and Services Administration projected that 50 states would experience a nursing shortage by 2015. In New York, the vacancy rate for nursing jobs was 6.38% in 2006, according to a survey conducted by the Healthcare Association of New York State.

The shortage has boosted starting pay for nurses in New York City, where graduates of a four-year nursing program can earn more than $60,000 annually. As a result, and thanks to aggressive nurse recruitment and retention efforts by hospitals, local nursing schools said enrollment is booming.

New York University’s College of Nursing expects 230 new students this fall, an increase of 50 from the spring semester, administrators said. Pace University currently has 770 nursing students, up from 450 five years ago.

“It’s the stability of a career in nursing, where you’re guaranteed, essentially, that you’ll have a job forever,” the dean of Pace’s Lienhard School of Nursing, Harriet Feldman, said.

At least one nursing student said the shortage inspired her to become a nurse. “I am honest with myself that it is a tough situation,” a student at New York University’s College of Nursing, Annmarie Campanella, said.

But industry insiders said current contract disputes reflect the challenges faced by nurses already in the workforce.

Two years ago, contract negotiations at Lenox Hill Hospital hit a snag over the hospital’s nurse-to-patient ratio, and the nurses came close to striking for the first time since 1988. Although an agreement was reached, officials at the New York Professional Nurses Union, which represents Lenox Hill’s nurses, said they are having trouble enforcing the contract.

“It’s attributable to a fundamentally broken system. And is it getting worse? It sure seems like it,” NYPNU’s executive director, Naomi Zauderer, said.

Some said the situation is impacting nurse morale. At Mount Sinai, which faced financial woes several years ago but bounced back, nurses said they thought they would have benefited from the hospital’s current financial health. The base salary for nurses at Mount Sinai is $66,023 a year.

“I think the nurses are a little put out,” a veteran nurse and the president of the union’s local bargaining unit, Marva Wade, said. “Reward and recognition are not just two words on a piece of paper.”