Mothers may have been underpaid their state pension by thousands of pounds and are being urged to check if they might be owed backpayments.
If mothers took time out of work to raise children since 1978, they should have had National Insurance credits that top up their state pension.
The idea is that these parents should not miss out on getting the full state pension because they want to have children.
This scheme is known as the Home Responsibilities Protection.
But many mothers may have smaller state pensions than they should have because of mistakes with their records, the BBC reports.
These mistakes mean many mums are missing out on National Insurance credits and are getting lower state pensions than they should do.
Pensions experts LCP have a tool that lets people check if they might be missing out on these credits.
Sir Steve Webb, former pensions minister and LCP partner, said: "Yet again, this error overwhelmingly affects women, and undoubtedly means that many thousands have been underpaid for years.
"Rather than wait for the Government to fix the problem, I would encourage anyone who has received child benefit since 1978/79 to check that the relevant credits are on their NI record.
"If not, this can be fixed by filling in a form, and the result could well be a higher pension and a worthwhile lump sum."
Webb said the issue first came to light ten years ago - and was meant to have been fixed.
But LCP has spotted new cases.
One case spotted by LCP is Lorraine Wainwright, 68.
Lorraine was given a backpayment of £1,500 and weekly state pension increases of around £20.
Wainwright said: "If I had not checked my own record carefully, it is quite possible I would still be getting the wrong rate of pension. I welcome this new campaign, which could help thousands of mothers to get their dues."
A Government spokesperson said: “This year we will spend over £110billion on the State Pension and support over 12.5million pensioners.
“We are investigating an issue with the historical recording of Home Responsibilities Protection, with work under way to identify those affected.”
Last month The Mirror reported that an investigation into a controversial increase in women’s state pension age has moved up a gear and will be sped up.
Around 3.8million women have lost up to six years in pension payments due to their retirement age rising from 60 to 65, now 66.
The campaign group Women Against State Pension Inequality, or WASPI, has been fighting against this inequality for decades.
But now the Parliamentary and Health Service Ombudsman published the findings of the first stage of an investigation last summer into the move to raise women’s state pension age to 65.
It judged that in 2005, the Department for Work and Pensions (DWP) "failed to make a reasonable decision about targeting information to the women affected by these changes".
It also said that in 2006 the DWP proposed writing to women individually to tell them about the changes to the state pension age, but "failed to act promptly," branding both "maladministration".
WASPI has long said that women born in the 1950s suffered financially from the 1995 Pensions Act and subsequent legislation, which raised the state pension age for women born on or after April 6, 1950.
The Ombudsman is now preparing the second stage of its investigation.
