Three nurses in the labor and delivery department at Mount Sinai Hospital have been fired for allegedly “sabotaging” emergency drills the hospital was running to prepare for the strike that began Monday, according to a spokesperson for the hospital.

The spokesperson, Lucia Lee, said the nurses were caught ahead of the strike, hiding medical supplies from temporary nurses who had been hired as their replacements.

“This is completely unacceptable behavior, which included locking critical supplies designed to care for vulnerable newborns in conference rooms where they did not belong,” Lee said.

The New York State Nurses Association, which represents the three terminated workers, denied the hospital’s allegations and said the firings were part of a pattern of retaliation and intimidation by Mount Sinai management in recent weeks as nurses geared up for the strike.

Thousands of nurses have entered their third day of striking at hospitals run by Mount Sinai Health System, Montefiore Medical Center and NewYork-Presbyterian as they fight for higher pay and improvements to health benefits, staffing and hospital security. The nurses have been without a contract since Dec. 31.

Contract negotiations have been paused since Sunday, but nurses are scheduled to go back to the bargaining table with NewYork-Presbyterian Thursday evening and with all hospitals on Friday, according to the New York State Nurses Association.

The Nurses Association submitted unfair labor practice charges against Mount Sinai to the National Labor Relations Board on Tuesday on behalf of the three labor and delivery nurses who were terminated. The filing says the nurses were fired via voicemail hours before the strike began and attributes the move to the hospital’s “anti-union animus.”

“It was Mount Sinai’s cruel attempt to stop us from joining the strike line and to make an example of us to our fellow nurses,” Liliana Prestia, one of the fired nurses, said at a rally outside Mount Sinai Hospital on Tuesday. “But we are not scared, we will continue to fight.”

The union has filed half a dozen additional charges against Mount Sinai with the National Labor Relations Board since October, alleging retaliation, intimidation, surveillance and interference with protected union activities.

According to the union, other Mount Sinai nurses were disciplined for speaking out to the media and colleagues about demands for greater hospital security after a man with a gun was apprehended at Mount Sinai Hospital in November.

Lee said those nurses were disciplined for distracting from patient care. Lee said accusations of “union busting” by Mount Sinai were “false.”

Mount Sinai says the more than 1,400 temp nurses the system has brought in during the strike have allowed the affected hospitals to provide ongoing patient care. However, the Nurses Association argues that the money hospitals are spending on replacements should be allocated toward meeting union demands.

According to the Nurses Association, nearly 15,000 nurses are striking across hospitals. Lee said about 20% of unionized nurses at Mount Sinai have come in during scheduled shifts so far, however.

This story was updated with new information on when negotiations are scheduled to resume.