Sports Direct boss Mike Ashley has been urged to send "scared" warehouse workers home over fears they are spreading coronavirus.
The Unite union said staff - including those with underlying health conditions - were warned they would lose their jobs if they stayed at home.
Some who spoke to the BBC said working conditions at the firm's base in Shirebrook, Derbyshire, were not safe.
Sports Direct has not responded to requests for comment.
Earlier this week it agreed to close its physical stores, a U-turn after the company previously argued it provided an essential service and should stay open.
However, people can still order online, and the firm's web orders are processed at its Shirebrook distribution centre.
There are fears workers could spread coronavirus to ex-miners in the local community who have severe chest problems.
Products 'not critical'
In her letter to management, Unite regional officer Cheryl Pidgeon said: "For the sake of the employees, the local community and the business reputation please allow workers to go home, stay safe and pay them their usual wages without loss of money."
Her concerns included:
- Workers not staying 2m (6ft 6in) apart in line with social distancing measures
- Claims of a lack of cleaning products
- Reports of staff being told to drive to work with five people in each car
"The products that many people are working on are not critical to the nation at this moment in time," she said.
"There are many, many scared workers at the warehouse."
One worker told the BBC that thousands of staff stand close together when clocking in and out, and the screens they use to do so were not being wiped.
"There are queues, shoulder to shoulder at the clocking in and out screens and down the stairs, picking equipment isn't sterilised, lots of people are close together in the toilets and canteen, with no-one monitoring distance," the worker said.
"I'm frightened the virus is being taken back to Mansfield and Shirebrook."
Another worker said: "I was scared; there is no chance to keep distance when pickers come around. You even touch each other.
"I don't feel safe where I was working with online orders."