Mike Ashley, the billionaire founder and majority owner of Sports Direct, told lawmakers in June that the firm had effectively paid staff at its Shirebrook warehouse in Derbyshire, central England, below the statutory minimum wage by requiring them to queue for security checks on their own time.

Ashley said he would fix the failings.

Unite said the payments, backdated to May 2012 for direct employees and agency workers, cover time taken for unpaid searches at the end of shifts and could be worth up to 1,000 pounds for some workers.

"This is a significant victory in Unite's ongoing campaign to secure justice and dignity at work for workers at Sports Direct and demonstrates the importance of modern trade unions in Britain today," said assistant general secretary Steve Turner.

The union is urging Sports Direct shareholders to back a resolution at its annual meeting on Sept. 7 for an independent review into work practices at the retailer.

Sports Direct was not immediately available for comment.

(Reporting by James Davey; Editing by Keith Weir)