Tens of thousands of women are missing out on a state pension because of rules affecting part-time staff, experts say.
The Pensions Advisory Service says people who earn less than £95 per job - no matter how many positions they hold - do not get pension credits.
It says such staff are often women who could boost future entitlements by making small changes to their jobs.
The government says reforms will make pensions fairer and more generous for women from 2010.
Until then part-time workers can make voluntary contributions to build up credits, it adds.
Entitlement to the full state pension is based on the number of National Insurance contribution credits made by workers or those on certain state benefits - currently 44 years for men and 39 years for women.
Women who have at least 10 years of contributions will usually be entitled to a reduced pension.
The Pensions Advisory Service, an independent voluntary organisation grant-aided by the Department for Work and Pensions, says only a third of woman currently get a full state pension.
It says many women work in low paid part-time jobs and therefore miss out on National Insurance contributions.
Malcolm McLean: "There could be tens of thousands of women... missing out"
Contributions are not payable on earnings less than £110 a week but those who earn between £95 and this level are given a credit towards a pension by the government.
Malcolm McLean, chief executive of the Pensions Advisory Service, says a small pay rise could be worth thousands of pounds in a future larger state pension.
"There could be thousands of women earning less than £95 a week either in single of multiple employments who are unaware that by increasing their hours or work slightly and increasing their pay up to the lower earnings limit neither they nor the employer will be required to pay National Insurance contributions but they will be treated as having paid them."
From 2010, both men and women will need to have paid contributions for 30 years to claim a full state pension.
Pensions minister Angela Eagle told the BBC the reforms will mean 75% of women will start getting a full state pension.
She added that carers will also start earning credits towards a pension from 2010.
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