Sports Direct faces a fresh legal challenge over its zero-hours contracts after 250 ex-employees joined forces to object to being excluded from a bonus scheme.

The part-time staff who worked on zero-hours contracts between April 2008 and August last year are taking part in legal action in the High Court after allegedly being barred from a payout of £160m of shares to 2,000 permanent employees last year.

Leigh Day barrister Elizabeth George, who is representing the workers, told the Guardian: “These are the staff whose hard work over many years has brought about the record profits that funded the bonus awards in the first place. It’s plainly unfair that they should have missed out.

“We believe that they had a contractual right to the bonus because regardless of the zero-hours label that the company has given their contracts, they were all permanent employees of the company for the necessary number of years.”

Pay Justice, the workers’ rights group, is urging more staff who believe they may be entitled to compensation to contact them via the website.

Sports Direct is unable to comment on the legal action because of another case involving a former employee that is due to go before the courts later this autumn.

Ex-employee Zahera Gabriel-Abraham is bringing an employment tribunal against the retailer to test the legality of its treatment of part-time staff on zero-hours contracts.

Gabriel-Abraham is also being represented by Leigh Day and supported by campaigns group 38 Degrees. She will argue there are no practical differences between obligations put on zero-hours workers and full-time employees.