A future coalition government may not overturn a means test on the private health insurance rebate.
The Gillard government is set to limit the 30 per cent rebate and increase the Medicare levy surcharge for those without cover.
Labor appears to have won the support of three crossbench MPs to get its twice-failed legislation through parliament's lower house, possibly as early as next week.
The coalition opposes the changes, which would apply a means test for individuals earning more than $80,000 and couples earning more than $160,000.
But Opposition Leader Tony Abbott would not commit a coalition government to overturning any means test.
'We're going to fight it,' he told reporters in Melbourne on Friday.
Pressed on whether the coalition would reinstate the rebate without a means test, Mr Abbott said, 'Ask me that question if we come to that situation.'
Earlier on Friday, opposition health spokesman Peter Dutton was not prepared to say the means test would be overturned.
'We're looking at a number of measures at the moment which may further enhance the attractiveness of private health insurance,' he told ABC Television.
'There may be smarter ways that we can do that.'
Deloitte research cited by the opposition indicates that if the means test clears parliament some 1.6 million Australians will drop private hospital cover over the next five years and another 4.3 million will downgrade their cover.
The government disputes those figures, saying Treasury modelling suggests only 0.3 per cent, or 27,000 people, will drop out of the private system.
Nationals leader Warren Truss said the means-testing of the rebate was a broken promise by Labor.
'True to form, this prime minister, her predecessor and the current health minister are at it again, betraying the trust of Australians,' he said in a statement.
As shadow health spokesman, Julia Gillard said in 2004 Labor would leave the 30 per cent private health insurance rebate 'undisturbed because we understand it's factored into family incomes'.
Former prime minister Kevin Rudd said in 2008 that the private health insurance rebate 'remains unchanged and will remain unchanged'.
In 2009 former health minister Nicola Roxon, now attorney-general, said the government was 'firmly committed to retaining the existing private health insurance rebates'.
Health Minister Tanya Plibersek said the opposition needed to come clean on whether it would scrap the proposed changes.
If the amendments were repealed it would add another $2.4 billion to the coalition's estimated $70 billion in savings it wanted to find.
'This is just the latest example of how the opposition are a laughing stock when it comes to the economy,' Ms Plibersek said in statement.
Couples would have to be earning $258,000 a year or more in the next financial year to lose the rebate altogether, she said.
