Sports Direct has come under fire after a report revealed that 90% of the high street retail firm's 23,000 employees were on controversial zero hours contracts.
The criticism comes after Sports Direct were praised for its shares for staff scheme.
The programme is saw thousands of pounds in dividends paid to full-time staff, who are shareholders under the initiative, as the company's annual profit soared 40% to £207.2m (€240m, $319m) in the year to 28 April.
However, according to a report by the Guardian, the sports retailed owned by billionaire Mike Ashley places most of its staff on zero hours contracts, which deprives them the security and rights of regular full-time employment.
Zero hours contracts leave staff unaware of how much they will work and earn from one week to the next and does not include sick and holiday pay.
"This is yet more evidence of how rife zero hours working has become across the economy," said Frances O'Grady, general secretary of the Trades Union Congress (TUC).
"The government needs to get tough with those employers who use workers on the cheap by getting them employ to people on secure contracts with decent wages."
At the time of publishing, Sports Direct had not yet replied to IBTimes UK's call for comment.
Zero Hours Contracts Under Government Review
In June the UK government started a review into the use of zero hours contracts by the country's firms. According to the Office for National Statistics, there are around 200,000 workers on zero hour contracts in the UK.
Many businesses say they need the labour flexibility that comes with such contracts because they cannot guarantee work all of the time, and so cannot afford to take people on for a set amount of hours each week.
"While we are pleased that ministers have launched a review into zero hours contracts this must lead to proper regulation to prevent their continued misuse," said the TUC's O'Grady.
Labour's shadow business secretary, Chuka Umunna, said that Labour is looking at how it can regulate the use of zero hours contracts under its policy review.
"The abuse of zero hours contracts is unjust and unacceptable," he tweeted.