Allowing low-income earners to opt out of compulsory superannuation would be a "despicable attack" on people's future retirement, Labor says.
The Turnbull government is reportedly being urged to consider the "opt out" idea in pre-budget submissions by industry groups.
The move could give thousands of part-time and casual workers earning less than $37,000 a 9.5 per cent pay rise - the amount paid by employers into superannuation - or up to $63 a week, News Corp reports.
"This is a despicable attack on the very foundations of a decent retirement for working Australians," Labor's superannuation spokesman Jim Chalmers told reporters in Brisbane on Sunday.
"The Liberal Party has never believed in compulsory superannuation and ... already they've frozen the superannuation guarantee, they're abolishing the low-income super contribution and these revelations today show that they plan to go even further."
Deputy Prime Minister Barnaby Joyce declined to comment but said low-income workers more than likely would end up on the pension.
He wanted to encourage younger people to invest in the housing market, particularly in regional areas where houses were cheaper.
"By the time of retirement ... they receive the pension and own the house they are in. They are in a better position than most," he told Sky News.
Mr Joyce attacked Labor's plan to limit negative gearing to new properties from mid-2017 should they win this year's federal election.
The opposition argues it would result in more affordable housing, but Mr Joyce says it must also then reduce the value of properties that people already own.
Those with a mortgage could suddenly find the value of their home was less than the money they borrowed from the bank, he said.
Dr Chalmers described the comments as a "desperate and unhinged scare campaign", long on dishonesty and short on fact.
News Corp also reports the government's own considerations on negative gearing include exempting "mum and dad property investors" claiming deductions under $20,000 a year.
The government has said only that it will release its much-anticipated tax package before or at the time of the May budget.
Treasurer Scott Morrison was widely criticised last week for a lengthy speech that gave a broad outline on what he wanted to achieve in the budget and on tax reform, but was light on specifics.
Deputy Liberal Leader Julie Bishop defended the treasurer's approach, saying every responsible government in living memory had laid out their economic and tax agenda at the time of the budget.
One exception was the Kevin Rudd-led Labor government in 2010, which commissioned the Henry tax review, discarded most of its recommendations except the mining tax, announced that prior to the budget and it was an "absolute disaster".
"So we are being methodical, logical, responsible, and in accordance with precedent," she told ABC television.
