The prospect of a breakthrough on the contentious tax treatment of superannuation earnings has moved a step closer with Labor extending a rare offer of bipartisanship to a cash-strapped government.

With Treasurer Joe Hockey this week inviting a national conversation on tax reform, and struggling to craft a budget amid a declining revenue outlook, Labor's Chris Bowen has offered support for a crackdown on the super incomes of the super rich.

It would likely apply to those with millions of dollars sitting in superannuation accounts from which they derive tax-free six-figure annual salaries.

"The Labor Party believes the taxation treatment of superannuation is unfair and needs to be fixed," Mr Bowen said in Melbourne.

"I pointed out that this could be a matter of some bipartisanship if the government chose to agree as part of this so-called national conversation."

The Shadow Treasurer cited figures provided by the industry body, the Association of Superannuation Funds for Australia.

"ASFA shows, for example, that there are 475 people with more than $10 million in their superannuation accounts earning $1.5 million in income and there are 100,000 people in Australia with superannuation balances in excess of $2 million," he said.

"This is a real issue which needs to be addressed. The Labor Party is prepared to lead the way."

One possibility is that Labor could support new tax arrangements for high-end super fund accounts in exchange for a commitment from the government to recommence the staged progress toward a 12 per cent compulsory employer-funded superannuation goal, which has been paused by the government.

Because of the favourable treatment of superannuation, revenue forgone in concessional tax rates - mostly 15 per cent on contributions rather than the relevant marginal income tax bracket - is extremely expensive, currently costing the budget more than $35 billion annually.

The government is wary of even discussing superannuation rules after promising in iron-clad terms before the election that there would be no negative modifications to the oft-tampered-with rules during its first term.

However, it is increasingly becoming accepted that the generous concessions for super at the top end have no utility in public policy, because they do nothing to keep people of such obvious wealth from claiming the age pension for which they are not eligible anyway - the original purpose for the concessional treatment.

Assistant Treasurer Josh Frydenberg has acknowledged that superannuation does need to be discussed as part of the broader tax mix, albeit with any changes to occur in subsequent terms of parliament.

"At the same time we need to be very conscious of the fact that we made that commitment at the last election that there'd be no adverse or unexpected changes to super and that we need to look right across the board and not just, as the Labor Party likes to do, at the higher income earners," he said.

His predecessor in the role, the respected NSW senator Arthur Sinodinos, has also acknowledged that some action needs to be taken on "equity grounds".

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