The retailer is cutting benefits to shop staff such as premium pay on Sunday and Bank Holidays following the introduction of the national living wage and an increase in its basic rate of pay for staff. It is also moving employees out of its defined benefit scheme.
M&S' accounts reveal the bill for the changes will come to between £100m and £150m.
M&S also announced in September that it would be cutting 500 staff from its head office, which will result in a charge of £10-15m for the business.
The so-called transition payments were increased after pay discussions between the management and staff. The retailer came under criticism for its conduct during the consultation, and was accused of threatening to sack staff who rejected the new contracts.
A spokesperson for Marks and Spencer said: “As we said in May and again in September there will be a non-underlying charge in the current financial year for the pay and pension changes in the range of circa £100m to £150m and the charge will be largely driven by the DB pension changes.”
A group of 70 MPs requested to meet M&S boss Steve Rowe to discuss the changes he was making for his staff, asking if he would also be willing to take a pay cut. But he refused to meet them.
Speaking to City A.M., one employee, who wished not to be named, said staff in the head office are "very concerned about the future".
"Most store staff have signed the new document around pay and pension as they are worried about losing the pay off and the termination of their job," the M&S employee said.
"The feeling of most people affected is that this is just the start and they are worried about what is next."
Siobhain McDonagh MP, who has been campaigning for M&S employees, said: "After our campaign, M&S did announce a very marginal change in their transitional payments, but still these changes fell far short of what longstanding employees truly deserve.
"Since myself and over 70 MPs wrote to Steve Rowe to express our concerns, we have been extremely disappointed that he has consistently refused to meet with us directly to discuss M&S’s plans. And since then, we have discovered that M&S plans to make its redundancy notices the week before Christmas – a very festive gift from the company. M&S is trying to run away from the mess it has caused – but it can’t hide."