Nurses at two of New York City's biggest hospitals are on the third day of their strike over contract negotiations.

More than 7,000 nurses from Mount Sinai Hospital in Manhattan and Montefiore Medical Center in the Bronx have participated in the walkout this week. They're demanding not just salary increases, but improved staffing levels.

"Bosses have pushed us to strike by refusing to seriously consider our proposals to address the desperate crisis of unsafe staffing that harms our patients," said the New York State Nurses Association, the union representing the workers.

There are hundreds of unfilled nursing positions at the two striking hospitals, WNYC reporter Caroline Lewis told NPR on Monday. Many nurses, stretched thin by the COVID-19 pandemic, have left their jobs for more lucrative travel nursing roles or quit the profession altogether.

Striking workers say their hospitals have failed to hire and retain enough nurses, creating a staffing shortage that is reducing the quality of patient care. They've spoken of beds being left in overcrowded hallways and nurses being forced to care for some dozen patients at a time.

Staffing issues are not unique to New York City, with one Mount Sinai official calling it "a national workforce crisis." Plus, an aging population is straining the country's health care system as a whole: The U.S. Bureau of Labor Statistics projects that the U.S. needs more than 275,000 additional nurses from 2020 to 2030.

Jennifer Mensik Kennedy is the president of the American Nurses Association, a professional organization. Emphasizing that a strike is a last resort, she told Morning Edition on Wednesday that the actions being taken in New York "reflect the experiences and feelings of many nurses nationwide."

"What's going on today is that these work environment challenges have been predating COVID-19, and nurses have been experiencing many of these challenges for decades," she said. "And the current strain of COVID-19 and other public health emergencies have only worsened many of these existing challenges and issues."

She spoke with NPR's Dwane Brown about the roots of the problem and what it would take to solve it.

This interview has been edited for length and clarity.

Interview highlights

On the systemic issues that created staffing shortages

We've experienced shortages of nurses, historically, for many decades. And right now we have an aging population, we've got the baby boomers aging. We have many choices for nurses — for women — to go into other professions. And we have a lack of faculty who are able to bring those nursing students in. We had ... many people who wanted to go into nursing school, for instance, who were just unable to get enrolled into the nursing school because there's just not enough spaces ...

... Oftentimes, new graduate nurses will make more than their faculty who are teaching them. So we have to address issues like that. Why would someone want to come and teach if their new graduate nurses are going to make more than them right out of school?

On what hospitals can do to prevent shortages

We definitely need more nurses. But what we've found [over] decades of research and programs is that when we have really good work environments for nurses — where nurses are valued, nurses are listened to and nurses can provide quality, safe care — those hospitals, those organizations, don't experience the shortages that other hospitals do. There are solutions that organizations can put in place to attract nurses and retain nurses. And nurses will go to those organizations where they feel valued and they feel like at the end of the day, at the end of this shift, that they were able to provide good quality care to people.

On what a long-term solution would look like

The American Nurses Association shares the nurses' frustration with a lack of solutions. And we've really worked together with decision-makers in organizations and nationally to say, you know, we really do need to work through and address safe staffing issues. We need to look at how we can address getting more nurses to be faculty and address the faculty shortage. And we also need to look at the work environment and encourage nurses to stay nurses and not to leave the profession. And we want nurses to be nurses for their entire career. So those are the three areas I think we could really focus in on in order to make a sustainable change.

The audio for this story was produced by Julie Depenbrock and Chad Campbell, and edited by John Helton.