Sports Direct came under fire again this week after MPs attacked its employment record in Parliament.

Former shadow business minister, Chuka Umunna, blasted the retailer as “a bad advert for British business” and said it had “a culture of fear in the workplace that we would not wish to see repeated elsewhere”, the Guardian reported. He submitted an urgent question on the wage position at the retailer that led to a debate.

It follows days of revelations in the Guardian, which plastered Sports Direct on its front page after an investigation by the newspaper claimed to have found that thousands of the retailer’s workers were receiving hourly rates of pay effectively below minimum wage.

HMRC has been urged to investigate Sports Direct, which has been accused of submitting its staff to unpaid security checks. The Guardian also claimed Sports Direct staff were too frightened to ask for time off even if they had to look after sick children that had been sent home from school ill.

Around £600m has been wiped off the value of the company in the last four trading days after shares slumped 16%. Mike Ashley’s personal fortune has tumbled £330m.

In Parliament yesterday business minister Nick Boles said: “I don’t care how famous an employer is. I don’t care how well connected they are. I don’t care, frankly, how much money they have made. They need to obey the law. If they don’t obey the law, we will find them and disqualify directors if necessary.”

Last week the Institute of Directors branded it a “scar on British business” and shareholders are beginning to express concern at the mounting pressure on Sports Direct and its business practices, the Guardian reported.