Parts of the federal budget could be ditched within months as the government concedes it might need to offer other savings to get some of its new measures through the Senate.
Treasurer Joe Hockey will outline the coalition's plan for business and families on Tuesday, but will have little new to announce after weeks of leaks.
The government will need to persuade six crossbench senators, the 10 Greens or the Labor opposition if it wants to pass budget spending, all of which will be matched by savings.
Prime Minister Tony Abbott says the budget's centrepiece - the jobs for families package - is based on savings, including an end to parental leave "double-dipping" and the passing of stalled family tax benefits changes left over from 2014.
"We're prepared to talk to the Labor Party and the crossbench about where these savings will be found, but savings must be found for this to go ahead," he said on Monday.
The government's savings were "justifiable and desirable", but if the Senate won't co-operate then other offsetting savings need to be found.
Opposition Leader Bill Shorten said Labor wanted to see the fine print before committing to any legislation, but the family tax benefit cut-off and parental leave change were unfair "thought-bubbles".
Both Labor and the Greens offered a crackdown on high-income superannuants and tougher tax checks on multinationals as optional savings.
Mr Hockey will unveil draft laws to deal with 30 of the worst culprits in seeking to hide earnings offshore.
Greens leader Richard Di Natale said his party would consider supporting the childcare package if it was not linked to the parental leave and FTB measures.
But the Greens would not support the coalition "balancing the books on the back of this country's most vulnerable people", he said.
The government also faces unrest from within its own ranks with Nationals senator Matt Canavan voicing concerns stay-at-home mothers miss out in the coalition's package.
"We are not afraid of making sure our voice is heard," he said, declining to rule out crossing the floor.
Independent senator Jacqui Lambie supports ending double-dipping, which allows parents to access both government and their own employer schemes.
But she would reject "anything and everything that is not going to be good for the nation".
Another crossbencher Nick Xenophon said the coalition had been more consultative with its second budget, after the disaster of last year.
"I don't think the government wants it to be a case of groundhog day, or night."
The prime minister and Mr Hockey came close to being shown the door at February's Liberal party room spill and continue to face political pressure before the crucial post-budget sales pitch.
Mr Shorten said Social Services Minister Scott Morrison, who undertook a flurry of interviews on Monday, had been doing Mr Hockey's day job "in a burst of impatience".
However, Mr Hockey said: "It's the government's budget ... we all work together, as we should."
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