ACT Senate candidate Simon Sheikh will make the announcement at a candidates' forum hosted by the Superannuated Commonwealth Officers' Association.

Mr Sheikh said Commonwealth public servants and Defence Force retirees have had their superannuation payments increase on average at only half the rate they should have.

''Over two decades, that could amount to more than $100,000 that each affected person is missing out on,'' he said on Monday.

"If I'm elected it will be one of my priorities to campaign for fairer indexation and I'll be joined by the rest of the Greens' team.''

The Greens will begin by releasing a policy to allocate an initial $2 million to commission the Australian Bureau of Statistics to develop a fairer indexation measurement that accurately reflects the changing cost of living for Commonwealth superannuants.

In Australia there are about 300,000 former public servants and Defence Force members. About 30,000 of them live in the ACT.

Commonwealth superannuation pensions, civilian and defence, are indexed to the consumer price index. The aged pension is indexed to the highest of the CPI, male total average weekly earnings or the pensioner and beneficiary living cost index.

Under the Howard government, three Senate inquiries considered the indexation of superannuation pensions and recommended reviewing it to better reflect the true cost of living.

The Labor government commissioned yet another report in 2008, that recommended against changing the indexation arrangement.

Mr Sheikh said successive governments had not rectified the problem of unfair indexing, with the result that many retired Commonwealth and Defence Force personnel were struggling financially.

''There are tens of thousands of retired public servants in our community who live on their superannuation pension, often supporting a spouse or partner as well,'' Mr Sheikh said.

''With Commonwealth superannuation pensions not rising as fast as the cost of living, many in our community are missing out.

''Three separate Senate inquiries over the last 12 months have found that, due to the failure to correct a technicality, retired Commonwealth employees miss out.

"Superannuation pensions are designed to take the pressure off our social security system while ensuring retirees can maintain a decent standard of living during their retirement.

''But many of the 300,000 retirees who are on Commonwealth superannuation pensions are struggling to make ends meet.

"The average Commonwealth superannuant is living off $27,000. Often, this $27,000 has to stretch to support two people.

''In an expensive place to live like Canberra, this is often just not enough.''

Last month, The Canberra Times reported that tens of thousands of retired public servants were being mobilised in the lead-up to the election to press for better pensions.

Superannuated Commonwealth Officers' Association federal president John Coleman said then that it was unfair pensioners' incomes were not keeping up with the cost of living, in contrast to former MPs' pensions.

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

Mr Coleman said the average annual pension his members got was $27,400. The poverty line, as reported in June last year by the University of Melbourne, was $28,786 a year for a couple.

Linking pensions to the consumer price index was an insufficient method of keeping retirement incomes in line with real cost of living increases, Mr Coleman said.