Retail organisation Argos is to provide back pay to 37,000 current and former store employees after they were found to have been paid below the statutory national living wage rate prior to December 2016.
About a third, or about 12,000, of those affected still work at Argos.
In an internal note to employees, John Rogers, chief executive of Argos, said: "After we acquired the Argos business a year ago it was brought to my attention that, as part of a routine visit, HMRC had uncovered an issue with some of our Argos store systems and processes, which means that some colleagues have been paid below the national living wage".
They relate to workers not being paid for staff briefings that could happen before they clocked on, or for security searches after they had finished their shifts. For the first time, the list includes employers who failed to pay eligible workers at least the new National Living Wage, now £7.20 for workers aged 25 and over.
The national living wage is now set at £7.20 and is due to increase to £7.50 an hour from April 2017.
He said new processes had been introduced to ensure there could be no repeat.
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Rogers added that he was "very disappointed" to hear staff weren't being paid correctly and immediately launched an investigation.
As many as 37,000 Argos employees are set to receive a £64 payment after it was revealed there had been problems with staff payments.
Excuses for paying less than the national minimum or living wage included using tips to top up pay, docking wages to pay for Christmas parties and making staff pay for their own uniforms.
Topping the list was high street giant Debenhams, which was accused of failing to pay nearly £135,000 to an estimated 11,858 workers.