contractPressure is mounting on Mike Ashley and his Sports Direct empire over its use of zero-hours contracts for part-time employees, as the Unite trade union demanded a meeting with the billionaire businessman.

As 2,000 full-time staff at Sports Direct prepare to cash in bonuses of up to £100,000, it has been revealed that the company’s entire 20,000 part-time workforce are employed on zero-hour contracts, according to data from the Office for National Statistics.

Sports Direct hires every part-timer under a deal that denies them holiday or sick pay and cannot guarantee how many hours they will work each week.

The zero-hours contracts are in use despite the company introducing a generous bonus scheme for full-time staff. Full-time workers at Sports Direct are set to collect a bonus worth more than £70,000 in company shares next month.

Those on the contracts often find themselves unsure if they will have work from one week to the next. Although they are able to turn down work, many fear that doing so means they will not be asked again in the future.

Employment lawyers warn that the deal makes it difficult to manage family and childcare commitments, and presents problems when budgeting for household bills or trying to secure a mortgage.

However, organisations investigating the impact of the contracts claim the revelations show their use is far more widespread than indicated by the ONS.

Business Secretary Vince Cable announced an investigation into zero-hour contracts following ‘anecdotal evidence of abuse’ by employers – including those in the public sector. ‘Whilst it’s important our workforce remains flexible, it is equally important that it is treated fairly,’ he said.

James Plunkett, director of policy at the Resolution Foundation, said: “These new revelations show again that no one really knows how many workers are on zero-hours contracts – every official estimate seems to have drastically understated the scale of the issue. While it seems to us too early to ban zero-hours contracts, the case for reform is clear.”