WHSmith, M&S and Argos are among the retailers 'named and shamed' by the government for breaking the law on the minimum wage.
A total of almost 5million was outstanding to around 63,000 employees following a series of investigations by HMRC from 2017.
Companies which have fallen foul of the law have been ordered to repay what they owed, as well as being fined around 7million in total.
WHSmith was revealed to be the worst offender - failing to pay around 1million to 17,607 workers, according to HMRC figures.
The high street retailer blamed this on a "genuine error" related to company uniform policy in 2019. A spokesperson said this was rectified immediately with all employees reimbursed.
They added: "Following a review with HMRC in 2019, and in common with a number of retailers, it was brought to our attention that we had misinterpreted how the statutory wage regulations were applied to our uniform policy for staff working in our stores."
Lloyds Pharmacy also failed to pay more than 900,000 to almost 8,000 employers, HMRC found.
The company has been contacted for comment.
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