Boris Johnson has told Sports Direct boss Mike Ashley to “expect the consequences” if he does not obey the rules over his employees during the coronavirus crisis.
Employees had been ordered to continue turning up to work at his Frasers Group stores, which are closed to the public, during the pandemic.
Amid much public confusion, the Government has said employees can continue working in non-essential industries if social distancing can be safely practised.
But Mr Ashley has provoked a series of controversies after initially planning to open his stores despite them being included in the ban and hiking prices of sports equipment by more than 50%.
Frasers Group also told staff at Sports Direct and Evans Stores to “please continue to head into work as we have been instructed last night”, according to internal communications seen by the PA news agency.
Labour MP Chi Onwurah asked Mr Johnson during Prime Minister’s Questions what he made of the discovery that Mr Ashley was not doing “the right thing”.
The PM replied: “The instruction to the gentleman in question and indeed every business is to follow what the Government has said, to obey the rules or to expect the consequences.
“That is the best way to look after not just their employees but their businesses as well.”
Downing Street later said shops that breach lockdown measures could face unlimited fines.
Sports Direct also told staff, in a document seen by PA, details of home fitness lines being hiked during the lockdown.
In a separate exchange, Mr Johnson suggested laws could be introduced to tackle profiteering when asked whether he would criticise “the disgusting scourge of black market profiteering”.
The PM responded: “Yes indeed, and I think that profiteering is something that we should be looking at from a legislative point of view in this House as has happened before in this country.”
Labour leader Jeremy Corbyn later told MPs that coronavirus “can only be solved by people working together, and not against each other”.
“The corporations and giant multinationals which wield so much power in our economy, appear to have the ears of prime ministers and presidents worldwide, will always put private profit ahead of public good.
“Just look at the actions of Tim Martin, the chair of Wetherspoons telling his staff, who are paid very little while he has raked in millions, go and work in Tesco, instead of standing by them in their hour of need.
“Look at the attempts of Mike Ashley to keep his shops open, putting his staff at risk,” he said.
The PM’s official spokesman warned that the competition watchdog, the Competition and Markets Authority, is ready to act if businesses “seek to exploit consumers during the outbreak”.
“The Prime Minister is clear that we don’t want to see profiteering of any kind and traders must stop any excessive price increases,” the spokesman said.
Meanwhile, Business Select Committee chairwoman Rachel Reeves has written to Mr Ashley and Mr Martin calling on them to set out how they are supporting their workers.