Two Amazon warehouse workers reportedly died on the job and now, the company is being investigated by the U.S. Department of Labor for possible labor issues.

The online retailer giant received criticisms for its poor treatment of employees. The company rejected the request of forming a labor union in its Delaware center. Meanwhile, warehouse workers in Germany demanded a salary increase.

The latest labor problem Amazon faces involves two workers who died in two separate warehouses. The first case occurred in December 2013 in Avenel, N.J, when worker Ronald Smith got caught in between a conveyor system while sorting packages and was crushed to death. The second incident happened in June 1 in a Carlisle, Penn., warehouse; details of the case were not disclosed, Businessweek reported.

According to the Occupational Safety and Health Administration (OSHA) division of the labor department, the investigators saw violations revolving Smith's death, but did not hold Amazon responsible. Based on their investigation, Smith was hired by a staffing agency for temporary work in the warehouse. The department held five companies, including four staffing agencies and a contractor for the sorting operations, responsible for the death of the worker.

"Temporary staffing agencies and host employers are jointly responsible for the safety and health of temporary employees," Patricia Jones, director of OSHA's Avenel Area Office, said in the statement, quoted by the Los Angeles Times. "These employers must assess the work site to ensure that workers are adequately protected from potential hazards."

Amazon released a statement after being cleared of the incident stating "any accident that occurs in a facility is one too many and we take these matters seriously."

The Associated Press reached out to Genco, the contractor cited by OSHA but has not responded yet regarding the issue.

The four staffing agencies were based on Baltimore, New York, California, and Ohio.