At least six Amazon workers died after the roof of an Illinois warehouse fell in on Friday.Officials said the collapse was due to the warehouse being hit by a severe weather event.The head of a major workers’ union said it was “inexcusable” Amazon required staff to work.

Amazon should not have had staff working at an Illinois warehouse when a tornado caused its roof to collapse, the head of a major workers’ union said.

The roof of the facility in Edwardsville fell in on Friday evening, leaving at least six workers dead. Local officials said the collapse was caused by extreme weather events.

“Time and time again Amazon puts its bottom line above the lives of its employees. Requiring workers to work through such a major tornado warning event as this was inexcusable,” the president of the Retail, Wholesale and Department Store Union, Stuart Appelbaum, said in a statement released Saturday.

“This is another outrageous example of the company putting profits over the health and safety of their workers, and we cannot stand for this. Amazon cannot continue to be let off the hook for putting hard working people’s lives at risk. Our union will not back down until Amazon is held accountable for these and so many more dangerous labor practices,” he added.

An Amazon spokesperson told the Associated Press when a site is made aware of a tornado warning, all employees are notified and directed to move to a shelter, but declined to answer, when asked by AP, when it warned employees.

Edwardsville fire chief James Whiteford said during a press conference on Saturday that a shift change had been underway when the collapse took place, Insider’s Bethany Dawson and Kelsey Vlamis reported.

Amazon did not immediately respond when contacted by Insider for comment about Appelbaum’s statement.

The RWDSU was involved in an effort earlier this year to unionize a warehouse in Bessemer, Alabama.

The workers in the Bessemer warehouse voted against forming a union with the RWDSU in April, but the National Labor Relations Board ordered a second election for workers in November saying Amazon had made “a free and fair election impossible.”

Amazon was not the only employer to have staff working during the severe weather events that ripped through Arkansas, Illinois, Tennessee, Kentucky, and Missouri this weekend. Kentucky Gov. Andy Beshear said he fears over 50 workers at a candle factory may be dead after it was hit by a tornado on Friday.