The House Committee on Oversight and Reform has opened an investigation into Amazon’s labor practices during severe weather events, according to a letter members sent to Andy Jassy, Amazon’s chief executive.

“We are concerned by recent reports that Amazon may be putting the health and safety of its workers at risk, including by requiring them to work in dangerous conditions during tornadoes, hurricanes and other extreme weather,” said the letter, signed by the committee chairwoman, Carolyn B. Maloney, as well as Representatives Cori Bush and Alexandria Ocasio-Cortez.

The investigation will focus on the December tornado that hit Amazon’s delivery station in Edwardsville, Ill., killing six people. Most people at the facility were not Amazon’s direct employees. They were subcontracted delivery drivers, a complication that impeded the response when the authorities could not readily determine how many people were on site. The facility did not have a tornado safe room, which was not required by building code.

At least one subcontracted driver was told to keep delivering during the storm, according to text messages Bloomberg News published. Amazon said the subcontractor’s dispatcher did not follow its safety protocols.

Amazon did not respond to an immediate request for comment.

Amazon’s labor practices have come under increasing scrutiny as it has grown to become the country’s second-largest private employer, after Walmart. The company employs 1.1 million workers directly in the United States, plus many more through contractors.

The letter asked Amazon for documents and communications related to how it managed its work force during several natural disasters, including fires in California, a heat wave in the Pacific Northwest and Hurricane Irma in Florida.

“This investigation will inform legislative efforts to curb unfair labor practices, strengthen protections for workers and address the effects of climate change on worker safety,” it said.