Prime Minister Malcolm Turnbull has defended the government's changes to superannuation in the wake of an attack from rival conservative parties.
Family First and the Liberal Democrats, both of which are seeking to retain their Senate seats at the election, are urging the government against making the changes retrospective.
They also say it breaches a coalition promise not to make any adverse changes to superannuation.
The minor parties' views are backed by groups such as the Institute of Public Affairs.
Mr Turnbull conceded in Sydney on Thursday the super changes did reduce generous tax concessions to people on very high incomes with large super balances.
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But they also made the system fairer and helped people on low incomes.
"Yes, people with more than $1.6 million in their super account will pay a little more tax - that is about one per cent of the population," Mr Turnbull said.
"But it's still a very low tax.
"Super remains a very attractive investment and we make no apologies for making the super system fairer and more sustainable over the years ahead."
