About 1,500 nurses are threatening to go on strike at Lenox Hill Hospital on the Upper East Side and two of its sister sites in Manhattan if owner Northwell Health doesn’t accede to demands to boost pay and improve staffing.

Unionized nurses at Lenox Hill, Lenox Health Greenwich Village, and Manhattan Eye, Ear and Throat Hospital said they gave Northwell notice of a potential strike on Wednesday and are planning to walk off the job at 8 a.m. on Nov. 4 if contract negotiations don’t move in the right direction.

If a strike occurs, the three facilities “will remain fully operational, ensuring that our patients receive uninterrupted, superior service,” Northwell Health spokesperson Barbara Osborn said in a statement.

The New York Professional Nurses Union began negotiating a new contract with Northwell Health last month on behalf of nurses at the three sites and are aiming to reach an agreement by the time their current contract expires on Oct. 31. But union representatives say negotiations have been difficult. Members voted almost unanimously to approve a preliminary strike authorization, the union announced Tuesday.

Nurses at other city hospitals have negotiated new contracts in recent years that have bolstered their salaries and left Northwell nurses behind, said Kathleen Flynn, president of the New York Professional Nurses Union.

“We need to reward longevity and get parity with the hospitals in the area,” Flynn said.

Northwell nurses are also fighting to reduce the number of patients they’re responsible for and hold onto existing staffing protections, said Niamh Girdusky, a medical intensive care nurse at Lenox Hill.

She said there are currently requirements in the union contract that nurses can only be asked to temporarily “float” to a different part of the hospital to fill a gap in staffing if they are clinically competent in that area. But she said Northwell is trying to loosen the rules.

“Nursing is already such a stressful job because you're holding lives in your hands,” Girdusky said. “When you're being sent somewhere that you are not comfortable working, that nervousness and that stress increases your risk of making a mistake tenfold, which is every nurse's worst nightmare.”

Asked about union demands regarding staffing and pay, Osborn said Northwell continues to negotiate with the union in good faith.

“We remain committed to reaching a fair and equitable contract that supports our nurses and maintains the high quality of care our community deserves,” Osborn said. “We value our dedicated nursing team and the exceptional service they provide.”

Members of a different union, the New York State Nurses Association, went on strike for three days at Mount Sinai Hospital in Harlem and Montefiore Medical Center in the Bronx in January 2023 and won higher pay and more robust staffing requirements.

Those hospitals brought in temporary nurses to help keep the facilities running during the strike, but clinicians still described chaotic scenes as those who remained struggled to care for patients.

Nurses at Lenox Hill last walked out in 1988. After striking for about a week, they won pay increases and got rid of mandatory overtime requirements, the New York Times reported at the time.

Northwell Health, which took over Lenox Hill in 2010, is the state’s largest health care provider, with hospitals across New York City, Long Island and Westchester County.

The New York Professional Nurses Union has emphasized during negotiations that Northwell is not hurting for cash. The nonprofit health care provider brought in a nearly $200 million operating surplus in 2023. It also has a for-profit investment arm, Northwell Holdings, and recently launched a production company called Northwell Studios, which will focus on health care-related content, similar to the documentary Lenox Hill, which debuted on Netflix in 2020.