As the government faces an internal backlash over policies to rein in superannuation tax breaks, MLC said there was a need to limit tax concessions for the most wealthy retirees.

However, it also argued the system should have the over-arching aim of encouraging people to save enough for an "adequate" income in retirement, rather than to supplement or substitute the pension, as the government is proposing.

The wealth manager's definition of "adequate" is about 70 per cent of pre-retirement income, capped at roughly $95,000 a year for the sake of equity.

A key debate in retirement policy is what exactly is the purpose of super, which is something that is not clearly defined in law.

The lack of such a definition is blamed for regular policy tinkering by governments, alongside tax breaks that have allowed some very wealthy retirees to draw down a tax-free income and amass large amounts of wealth while paying minimal tax.

Earlier this year, the government accepted the financial system's inquiry that superannuation's objective should be to "provide income in retirement to substitute or supplement the age pension".

But MLC is ramping up pressure on the government for a more ambitious goal, arguing this would give people planning retirement greater confidence and lower the drag on the budget.

MLC's executive general manager of superannuation and investment platforms, Paul Carter, argued the government should aim for a "higher bar" than the present proposal.

"A successful retirement system should encourage Australians to save enough to support them in retirement to a similar standard of living that they enjoyed pre-retirement," he said in an interview.

He said there needed to be a "reasonable" limit how much people could draw down tax free in super. NAB says the limit should be about 70 per cent of twice average weekly earnings, or about $95,000.

Separately from the debate about super's overall purpose, the government plans to put a $1.6 million cap on how much could be put into tax-free retirement accounts, and a $500,00 cap on non-concessional contributions.

The changes are forecast to affect the top 4 per cent of  income earners but are deeply opposed by some in the Coalition, prompting predictions Treasurer Scott Morrison will water the changes down.

Mr Carter said the policies to rein super tax breaks of the government and those proposed by Labor were "broadly right".

It comes as a new survey of 2000 people by MLC found many retirees worry about outliving their savings and two-thirds of Australians believed they were not well prepared for retirement.

In a sign of the big gender gap within super, the survey found 57 per cent of women in retirement were concerned they might live longer than their savings would last, whereas only 32 per cent of men had this fear.