Britain’s largest supermarket chain Tesco underpaid almost 80,000 of its workers, the UK government has revealed, as it “named and shamed” dozens of companies for not paying the minimum wage. A total of 139 companies failed to pay £6.7 million ($9.1 million) to thousands of workers, the government said Thursday. The cases were investigated between 2016 and 2018. The current minimum wage in the United Kingdom is £8.72 ($11.91) for workers aged 25 and over. Tesco, which has more than 3,700 stores in the United Kingdom and Ireland and nearly 7,000 stores worldwide, was by far the worst offender. The retailer did not pay 78,199 workers the minimum wage, according to the list, owing them more than £5 million ($6.8 million). The supermarket chain said it is “extremely disappointed and surprised to have been included in this list,” saying it identified its failure to pay minimum wage in 2017 and informed the government at the time. “Back in 2017 we identified a technical issue that meant some colleagues’ pay inadvertently fell below the National Minimum Wage. We are very sorry this happened and proactively reported the issue,” Tesco said in a statement. “All our colleagues were reimbursed in full and we immediately changed our policies to prevent this happening again. In most cases the reimbursement was £10 or less,” it added. Pizza Hut was identified as failing to pay nearly £846,000 to 10,980 workers. Superdrug, one of Britain’s largest pharmacy firms, was also included in the list, accused of not paying 2,222 workers more than £15,000 ($20,475). Superdrug said in a statement that the error occurred in 2018. “As soon as we were notified, we swiftly reimbursed both current employees and leavers, working with HMRC [Her Majesty’s Revenue and Customs] to ensure they were fully compensated,” Superdrug said, adding its policy had since changed. “Paying the minimum wage is not optional, it is the law,” UK Business Minister Paul Scully said in a statement. “It is never acceptable for any employer to short-change their workers, but it is especially disappointing to see huge household names who absolutely should know better on this list.”