The Occupational Safety and Health Administration is investigating the deaths of three Amazon workers which occurred in Amazon facilities in New Jersey.

All of the workers died while on the job over the last few weeks.

The first death happened at the Carteret fulfillment center on Prime Day – July 13. Rafael Frias, 42, died of cardiac arrest. His family has said that conditions inside the warehouse played a part in his heart attack.

But Amazon has done its own investigation. The company says it doesn’t believe that the death was a work-related incident.

“We’re deeply saddened by the passing of our colleagues and offer our condolences to their family and friends. Each of these tragic incidents has affected our teams greatly and we are providing resources for families and employees who need them,” a spokesperson for Amazon wrote in a statement.

A second death occurred on July 24 at the Robbinsville facility. That worker reportedly fell and hit his head. A third died at the Monroe facility on Aug. 4. A cause of death has not been provided. The names of the two employees have not been released.

Workers at the Carteret center are not part of a union. But incidents like these have at times brought on calls for employees to consider unionizing.