The U.S. Department of Labor's Occupational Safety and Health Administration (OSHA) said that it will investigate a recent death at one of Amazon's fulfillment centers. On Dec. 4, 2013, a temporary worker in one of Amazon's New Jersey facilities was killed while working on the job, and OSHA said it has already cited five companies, including four staffing agencies and Genco, the contractor hired by Amazon that operates the fulfillment center. Another death occurred at another facility on June 1, which is the one OHSA is now investigating.

"Temporary staffing agencies and host employers are jointly responsible for the safety and health of temporary employees," OSHA director Patricia Jones said. "These employers must assess the work site to ensure that workers are adequately protected from potential hazards. It is essential that employers protect all workers from job hazards — both temporary and permanent workers."

OSHA said Genco was cited for the first death specifically because it knew that the facility was hazardous to employees but it didn't certify that to the new employees coming on board. In other words, Genco knew that death as a possibility but the staffing agencies that hired the temporary worker weren't made aware of it. The staffing agencies were cited for failing to check to see how hazardous the working conditions were before assigning a temporary worker.

It's unclear what companies will be cited in the death on June 1, though that's what OHSA will now investigate, and perhaps why Amazon is contracting companies that aren't doing due diligence before hiring workers.