Labour leader Ed Miliband has waded into Sports Direct - accusing the Shirebrook-based retailer of using ‘Victorian practices’ for hiring thousands of workers on zero-hours contracts.
Speaking at a conference in the West Midlands, Mr Miliband described the company as a “terrible place to work”.
Labour has claimed 17,000 of its 20,000 UK employees are not guaranteed regular hours, in a party pledge to scrap zero-hour contracts.
Earlier this year, Derbyshire police also confirmed an investigation had been launched after an Eastern European employee gave birth in a toilet at the company’s main distribution warehouse.
The baby boy was taken to King’s Mill Hospital, near Mansfield, before being transferred to a specialist neo-natal unit in Leicester, police said.
Police revealed that the mother, a woman in her 20s, had also received hospital treatment.
Staff working at the company later claimed that the woman, who was not identified, had been forced back to work after claiming she was unwell.
In his speech, Mr Miliband slammed what he called “a zero-zero economy - of zero-hours contracts and zero tax for those at the top”.
The company has faced severe criticism from local politicians over its employment practices - with the vast majority of staff at its Shirebrook site coming from Eastern Europe.
Staff have complained of draconian employment practices, including strip searches and a six-strike dismissal policy.
Local politicians have also criticised the company - owned by billionaire Newcastle United owner Mike Ashley.
Bolsover MP Dennis Skinner has previously said that unions need to be allowed into Sports Direct and called for all employees to be on staff, and not employed through employment agencies.
He said: “This is a stranglehold and it needs to end. There should be democracy for the people who work at Sports Direct, because in my mind Mike Ashley is nothing more than an old-fashioned type factory owner.”
Mansfield MP Sir Alan Meale said: “I have spoken to people who work there and I know that staff are in fear for their jobs on a daily basis.
“Mike Ashley is making hundreds of millions of pounds and he’s allowing people to work in these appalling conditions.
“In my opinion, Sports Direct need to either accept the working environment in this country or get out of the market.”
Sports Direct, one of the UK’s biggest employers, previously said it was continuing to review “core employment procedures”.
Zero-hours contracts do not guarantee regular work for employees. Sick pay is often not included although holiday pay should be, in line with working time regulations.