Amazon is facing questions over health and safety policies at a warehouse in the US state of Illinois after six workers died when the building was destroyed by a tornado.
"This never would have happened if they cared about lives over productivity," the sister of one of the victims commented on social media.
The company says its team had "worked quickly" in response to the tornado.
The roof collapsed as the storm hit the warehouse on Friday.
One of those who died, Clayton Cope, 29, spoke to his family on the phone shortly before the building in the town of Edwardsville, Illinois was struck.
Clayton's mother Carla, said she had called her son to warn him of the tornado's approach.
"We told him it looked like the storm was heading that way and that he needed to get to shelter," Carla told reporters.
Clayton's sister Rachel said she understood from the conversation between her brother and her parents that he and the other workers were not immediately told to shelter after the first warning siren sounded.
She posted an comment on Facebook calling for publicity around the firm's approach to health and safety.
"Everyone knows that all Amazon cares about is productivity," she wrote.
She said she didn't believe her brother would have died if the company "got them [the employees] to safety after the storm started to get bad and took it seriously".
"No-one would have been frantically getting to the shelter last minute and my brother wouldn't have had to help people get to the shelter and put his life at risk," she wrote.
"I want them to answer for this, I want this to be a starting point of places taking the lives of their employees seriously and treating them as more than a number."
This has raised several questions whether adequate shelter was available, if workers were advised to go there immediately, and whether the shifts should have gone ahead that evening at all, given the warnings of severe weather.
The Edwardsville site received tornado warnings between 8:06pm and 8:16pm local time before the tornado struck the building at 20:27, Amazon said in a statement.
The company said that the team worked "incredibly quickly" to ensure as many employees and partners could reach the "shelter in place" site.
Amazon said following a tornado warning company procedure was for all employees to be "notified and directed to move to a designated and marked shelter in place location".
The majority of the team had taken shelter at "the primary designated location", the firm said, but a small group had taken shelter in a part of the building that was hit by the tornado. "This is where most of the tragic loss of life occurred," Amazon said.
Amazon said it was donating $1 million to the Edwardsville Community Foundation as well as providing relief supplies including transport, food and water.