Asda is seeking to move staff onto flexible contracts which mean staff being paid more per hour, but losing paid breaks.
Supermarket group Asda has been accused of trying to disguise a pay cut for thousands of its workers by imposing voluntary flexible contracts on all staff.
Asda proposes increasing its basic hourly rate to £9 an hour from £8.21 and maintaining annual bonuses and pensions.
However, paid breaks would end and staff would have to work, if required, on bank holidays, apart from Christmas Day, Boxing Day and New Year’s Day.
Women occupy 74% of Asda’s lowest paid roles.
In a letter to Asda chief executive Roger Burnley Labour MP Siobhain McDonagh has claimed that many Asda staff will be financially worse off under the plans due to the loss of paid breaks, a shortened night shift and an end to overtime pay for bank holidays.
She claims the move could mean 2,700 staff will lose up to £500 per year, with a further 300 losing even more.
The GMB union has said it will fight any imposition of the contracts on its members. The contracts already exist on a voluntary basis.
Gary Carter, GMB National Officer, said: “Since Asda introduced its flexible contract two years ago, nearly 60% of employees have opted not to go on the new contract.
“These contract changes will affect nearly 60,000 members of staff and they cannot just be imposed from the top.”
Asda says the changes will bring it in line with industry standards. Its prospective merger partner Sainsbury’s made similar changes to its contracts last year.
The supermarket is one of several to be targeted for equal pay claims. In January the Court of Appeal ruled an equal pay claim against Asda could go forward.