Pressure is building on the coalition government to slow the rate of acceleration of the state pension age (SPA) for women.
In the spending review last year George Osborne announced the SPA will rise to 66 by 2020, rather than by 2026 under Labour's plans. The changes particularly affect women born in the early 1950s. Around 500,000 women's SPA has risen by one year and for 33,000 it has risen by two years or more.
The reform is included in the Pensions Bill, which is due its second reading in the House of Commons in the next few weeks.
However, 138 MPs have signed an early day motion (EDM) calling on the government to revise the timetable for raising women's SPA.
The EDM says the government has not kept to state pension commitments made in the coalition agreement. It adds the timetable contradicts the recommendation in the Turner Review to give 15 years' preparation time for any SPA rises.
A further 10,000 members of the public have signed a petition against the bill created by Unions Together.
In a private members' debate on the SPA rise, Teresa Pearce, Labour MP for Erith and Thameshead, described the government's plans as creating a "deeply unfair situation".
Pearce added it is unfair to set the SPA based on average life expectancy.
She said average longevity indicates women will still draw a state pension for 24 years as they did in 1995, but socio-economic factors cause life expectancy to fluctuate wildly. This means some women will receive state pension for only a short amount of time.
Responding to criticism, pensions minister Steve Webb said: "The current schedule for raising the SPA is incredibly slow relative to improvements in life expectancy.
"The Turner Commission recommended looking at a way of linking SPA to longevity, and the current schedule does not do that.
"The women most affected by the change will be the first to benefit substantially from the universal state pension, as at the moment they get on average £40 per week less than men."
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