The nurses say staffing levels at the hospital have become dangerously low. It's one issue they've raised with Trinity Health System, the company that owns St. Mary.
"We've been negotiating for a whole year," said Jim Gentile, who has worked as a registered nurse with St. Mary for 42 years.
Gentile says the problems started to arise about four years ago when Trinity took over ownership of St. Mary.
"They cut staffing. They cut supplies," Gentile said.
He and nearly 800 other nurses began the two-day strike on Tuesday, after negotiations with Trinity stalled.
RELATED: Nearly 800 nurses strike at St. Mary Medical Center in Bucks County
The negotiations began before the first wave of coronavirus hit the area. The talks were put on hold as nurses cared for patients.
"We went in there, we did our duty. We put our lives on the line," said Donna Halpern, a critical care cardiac nurse. "We told Trinity you need to get us more staff before the second wave hits. They didn't."
Trinity Health Services says it offered the nurses a deal with more money and more staffing, but the union rejected it.
"They were going to give the nurses a 5% raise," said Gentile. "The offer they gave us was 15% less than what they gave Mercy Fitzgerald in Delaware County."
According to the Pennsylvania Association of Staff Nurses and Allied Professionals, (PASNAP), 243 nurses have left St. Mary in the past two years. That amounts to a 30% turnover.
Nurses say many of their colleagues left for better-paying jobs at other hospitals.
The nurses who still work at the hospital say they are now experiencing dangerously-low staffing levels. Some nurses take care of up to seven patients at a time.
Beth Redwine, a nurse in the hospital's mother/baby unit, says proper staffing is essential so nurses can give patients the care they need.
Replacement nurses are taking care of patients while staff nurses are on strike.
The two-day strike will end Wednesday night, but the replacement nurses will stay at the hospital a while longer.
"(The hospital's) lawyers told they will lock us out for three more days until Saturday," said Gentile.
After that, there's the question of whether negotiations will resume.
There is no scheduled meeting between the two sides, but the nurses say they're willing to leave the picket line for the bargaining table.
"I'm hopeful we'll get back to the table and make some meaningful movement," said Redwine.
Trinity released a statement on Tuesday saying in part, "We remain focused on our patients, visitors, and colleagues, and ensuring that we maintain uninterrupted access to and from our campus."