They say it is unfair their income is not keeping up with the cost of living, in contrast to pensions for former MPs.

The campaign is being ramped up by John Coleman, federal president of the Superannuated Commonwealth Officers' Association.

The association represents former federal public servants while former and current serving members of the Australian Defence Force are represented by the Defence Force Welfare Association.

Around Australia, there are about 300,000 former public servants and defence force members, with about 30,000 in the ACT.

Mr Coleman met politicians in Canberra on Thursday to push the case for improved indexation of his members' pensions.

He told them the average pension paid to his members was $27,400, whereas the poverty line reported in June last year by the University of Melbourne was $28,786 per year for a couple.

Linking pensions to the Consumer Price Index was insufficient to keep up with the real cost of living increases, he said.

''I am trying to get both parties to realise … this issue affects more than 300,000 people, right across the country and about half of those people reside in marginal seats.

''There is an electoral opportunity for either party to seize.''

Mr Coleman said the CPI has not reflected actual price increases for years. ''It's adjusted downwards wherever there is a product improvement,'' he said. ''That means the CPI doesn't increase in line with actual prices, for example with a new motor vehicle. The price of the new vehicle might go up by 5 per cent but if the new model has a product improvement such as air bags, then the percentage increase in the price movement would be adjusted downwards to reflect the value of those air bags.''

Mr Coleman said the aged pension was benchmarked to movement in wages in 1998.

''Governments of both political persuasion have acknowledged the CPI is not an appropriate index for pensions, which is why the Coalition changed the way the aged pension is indexed back then,'' he said.

He said any politician who entered Parliament before 2004 would have their pension indexed in line with a higher benchmark than the CPI.

''Most of the politicians from both sides of Parliament who are making the decision not to give us what we say is a fair index, will have their pension indexed by movements in parliamentary salaries and allowances, so they have a double standard,'' he said.

Mr Coleman rejected arguments the country could not afford to give better pensions to former federal public servants.

The association will target Labor and Coalition marginal seats, where it estimates the number of affected voters - its members - exceeds the margin by which the seat is held.

Eden-Monaro, centred on Queanbeyan, has around 13,000 affected pensioners, Mr Coleman said.

He praised the lobbying done by Labor Member Mike Kelly, a former ADF member.