Superannuation groups are pleading for the $1.5 trillion sector to be quarantined from structural or one-off hits in the budget in May.
Labor MPs were tightlipped on Tuesday on the prospect of changes to super tax concessions for high-income earners, after the former minister Simon Crean said super should escape tinkering.
The SMSF Professionals' Association of Australia, which represents 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 on the tax on super fund earnings from 15 per cent to up to 20 per cent.
Chief executive of Industry Super Network David Whiteley said industry super funds, which represent 20 per cent of total funds under management but about half the Australian workforce, were concerned by the proposed abolition of the low-income tax offset under a Coalition government.