Pressure is mounting on M&S' chief executive Steve Rowe to cancel a pay cut for his staff as an online petition to block the plan has received nearly 20,000 signatures in three days.
The company is consulting its staff over cutting premium pay on Sundays, and cuts to pay for bank holidays and employees working at anti-social hours, which could hit 7,000 staff. M&S is also considering reducing pension contributions, potentially affecting 11,000 employees.
The online petition - titled "Don't make staff cuts to pay living wage" - has been started by an M&S employee, who says they have changed their name to avoid criticism at work.
The employee, who goes by the name Kate Simpson online, says M&S are "targeting their most loyal staff" with the cuts, and that management is making the changes to met its new obligation to pay a national living wage.
Simpson writes: "I have worked at Marks & Spencer to nearly 43 years. I started in the company as a sales advisor and was promoted to a manager for 39 years, working in a number of stores in different management roles.
"I have always been so loyal which is why it feels upsetting to have to speak out now."
City A.M. learned earlier this month that M&S has been accused of threatening to dismiss staff who do not agree to the changes. As part of the consultation with staff, M&S wrote in a Q&A sheet that "one option" open to the company would be to take "the technical step" of terminating contracts for those who don't agree with the changes, and offering "re-engagement on new contracts which include the changes."
The clothing and foot retailer is also proposing a pay rise for M&S customer assistants from £7.41 to £8.50 outside London, and £9.65 inside London, as well as pay increased for more senior staff. M&S say most staff will be better off under the new pay system.
MPs are also ramping up the pressure on M&S' management:
A spokesperson for Marks & Spencer said: "We believe our proposed new approach to pay and pensions would reward our people in a fair and consistent way, simplify and modernise our business and help us attract and retain the best talent so we can continue to provide great service for our customers."