The Government says it intends to press ahead with its timetable to raise the state pension age for women, despite the threat of a revolt by Conservative and Liberal Democrat backbenchers.
MPs of all parties have urged ministers to rethink plans to speed up the equalisation of the pension age for women and men amid warnings that hundreds of thousands of women have not had time to plan properly for their retirement.
However, the Department for Work and Pensions (DWP) insisted the changes will go ahead as planned, warning that any delay would cost the taxpayer £10 billion.
Under the Pensions Bill, which receives its Commons second reading on Monday, the state pension age for women will go up from 60 to 65 in 2018 - two years earlier than planned under Labour - rising to 66 in 2020.
The move has provoked intense cross-party opposition, with MPs warning it discriminates unfairly against women in their late 50s who will now have to wait longer than they had expected to receive their pensions.
Lorely Burt, the chair of the Lib Dem parliamentary party, said up to 500,000 women would be hit as they "won't have time to plan their retirement and many will be financially a great deal worse off".
For Labour, shadow pensions minister Rachel Reeves said that ministers should bow to public pressure and rethink their proposals, adding: "It is simply wrong to punish women by moving the goal posts at this late stage."
Senior Tory backbencher Sir Peter Bottomley predicted that the Government would have to back down and accept that the changes were unfair.
"It is right to raise the pension age, it is wrong to do it for a particular group so dramatically and at such short notice," he told BBC Radio 4's The World This Weekend.
But the DWP said ministers intend to push through the change as planned, with a spokesman saying: "The Bill will go forward without any changes to the timetable. If we delayed the move to 66, it would cost the taxpayer £10 billion and would be an unfair burden on the next generation."