National Australia Bank-owned MLC is urging the government to enshrine in law that the purpose of superannuation be to deliver retirees a similar standard of living to what they had when working, rather than a supplement to the age pension.

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.