Labor did not oppose the "10-per-cent-cap" rules when they passed Parliament in 2015 but Mr Shorten said yesterday that part pensioners had been unfairly treated by the government and that, if elected, Labor would review pension rules.

The government is facing a backlash to the cap, which has seen nearly 48,000 retirees, former public servants, firefighters, nurses and other government employees on public sector superannuation pensions have their Centrelink payments reduced under new rules from January 1 this year.

The outcry from retirees' groups over the cuts intensified this week after revelations that pensioners on the lower income brackets were bearing the brunt of the $465 million in savings over the next four years, and they have been lobbying politicians from both major parties to consider changing the policy.

But Social Services Minister Christian Porter was unwavering, saying the rules were changed to "inject greater fairness".

Opposition Leader Bill Shorten, campaigning in Darwin, pledged a review of pensions and superannuation if Labor is successful in the July 2 poll.

"We think the government's policies are really unfair on part pensioners," Mr Shorten said

"We think there will be a whole series of unintended consequences and unfairness and there is a whole lot of complexity in their measures.

"What we will do if we are fortunate enough to form a government after July 2, we will have a review of retirement incomes policy which puts pensioners, part pensioners and self-funded retirees at the centre of our deliberations."

But Labor stopped short of saying it would restore the money that had been cut.

Earlier in the day, Mr Shorten's shadow treasurer Chris Bowen said the fiscal situation meant the party would not "make unrealistic promises" to retirees.

Mr Porter said through a spokeswoman that the 10-per-cent cap was about greater fairness.

"As we have consistently said, the rules were changed to inject greater fairness, to ensure that people receiving incomes from defined benefits schemes did not enjoy an advantage over people receiving incomes from other sources such as superannuation," the spokeswoman said.

Data from the Department of Social Services revealed that nearly 60 per cent of retirees who have been hit with cuts to their benefits were on incomes of less than $41,000 a year or less, and thousands of pensioners were getting by on $600 a week or less, when the axe fell.

At the other end of the scale, it is unclear from the official data how many retirees were getting the annual pension payments of more than $120,000 used by the government to justify the changes, but just 30 singles were on incomes of $2000 a week or more and just 168 couples fell into that combined income bracket.