The Co-operative Group has announced it is to scrap its final salary pension scheme.
The business said it wants to change the basis for payments on its defined-benefit pension scheme.
The decision by the retail and financial services group will see all staff transferred on April 5 to a new scheme based on the average salary over their career.
The move, which means staff will no longer have their pension linked to the salary earned in the final year of work, has caused anger among trade union groups.
Ron Webb, national secretary for transport at the T&G union said: "This is not a good way to start 2006. The Co-op can be assured that we do not accept the closure of the final-salary scheme as a foregone conclusion."
The union said it would not rule out calls for a vote on industrial action.
