BackTo60, a group supporting women affected by an increase in the state pension age, has lodged a judicial review claim seeking to force the government to reverse its decision.
The application to bring a claim against the Department for Work and Pensions was lodged at the High Court on 30 July, according to campaign spokesman David Hencke.
A judicial review is a court proceeding in which a judge considers the lawfulness of a decision or action made by a public body. It can't be filed directly, the court needs to be asked for permission first.
Mr Hencke said the High Court hearing was "bound to be challenged by the government which is determined not to pay up, but ministers will have to justify their actions".
The movement, which claims to have 738,000 supporters, is being supported by a legal team led by renowned civil rights barrister Michael Mansfield and legal firm Birnberg Peirce.
Backto60, along with other campaign groups like Women Against State Pension Inequality (Waspi), are arguing against the perceived inequality and unfair treatment of women born in the 1950s who have experienced changes to their state pension age.
The groups claim that when the 1995 Conservative government's Pension Act included plans to increase the women’s state pension age to 65 – the same as men's – the changes were implemented unfairly, with little or no personal notice.
The movements also claimed the changes were implemented faster than promised with the 2011 Pension Act, and left women with no time to make alternative plans, leading to devastating consequences.
Backto60 is requesting the state pension age to kept at 60 for women born in the 1950s, but such a decision would cost £77bn and has previously been dismissed by the government.
The movement secured £20,000 in additional funding through a crowdfunding campaign in 14 days, which will be used to fund the legal action and further support the campaign.
maria.espadinha@ft.com
