Sportswear giant Sports Direct is facing a legal challenge over its widespread use of zero hour contracts.

Law firm Leigh Day, with the support of campaigns group 38 Degrees, is bringing an employment tribunal case against the sportswear retailer to test the legality of its treatment of part-time staff, which are all on the contract.

Former Sports Direct worker and 38 Degrees member Zahera Gabriel-Abraham has brought the legal claim funded by other 38 Degrees members through donations, according to the Press Association.

Leigh Day barrister Elizabeth George is arguing that the contract offers no flexibility to workers as there were no practical differences between the obligations put on Gabriel-Abraham to full-time employees.

38 Degrees said it had a “huge response” from its members on the issue of zero hour contracts.

Research by the Chartered Institute of Personnel and Development suggested that more than a million UK workers are signed up to the contracts, four times official estimates.

Sports Direct declined to comment.