Superannuation groups are pleading for the $1.5 trillion sector to be quarantined from structural or one-off hits in the May budget.
Senior Labor MPs were tight-lipped on Tuesday on the prospect of changes to super tax concessions for high-income earners, after former minister Simon Crean said super should escape tinkering.
The SMSF Professionals Association of Australia, which represents professional advisers to the self-managed super sector, said there was "growing speculation" Labor would reduce the threshold at which a 15 per cent tax on concessional contributions would apply to $180,000.
Legislation for the 15 per cent tax, which was introduced in last year's budget but targeted people earning more than $300,000, has yet to be introduced to Parliament.
SPAA technical director Peter Burgess said another rumoured change was an increase in the tax on super-fund earnings from 15 per cent to up to 20 per cent. "But this will have an impact on high and middle-income earners, so is considered less likely," he said.
Industry Super Network chief executive David Whiteley said that industry super funds, which represent 20 per cent of total funds under management but about half of the Australian workforce, were concerned by the proposed abolition of the low-income tax offset under a Coalition government.
He said about 3 million people, including about half of industry fund members, benefited from an offset, which applies to people with a taxable income below $66,667.