Senator Nick Xenophon has warned the Abbott government its "dumb" budget is toxic with a key component of the Coalition voter base.
"This has been called the toughest budget in decades, but it also seems to be one of the dumbest," the South Australian independent wrote in a budget appraisal.
"The 'Howard Battlers' that re-elected John Howard on four occasions won't cop these changes."
Senator Xenophon is one of eight crossbenchers who will hold the balance of power in the Senate from July 1.
In a veiled warning that he will not vote for key measures, including cuts to welfare and the dole, Senator Xenophon urged the government to consider a rapid rethink, headlining his analysis: "Budget is mean, nasty and dumb".
"This budget has shocked me, but it's the government that could expect a bigger shock unless it tackles the manifest unfairness in its budget," he wrote.
"How on earth is it fair that a single mum with three kids is going to be $3000 a year worse off than someone on $300,000 a year who is being let off relatively lightly by paying $2400 in a deficit levy for three years.
"None of us want welfare to be abused but the government is implying that all Newstart recipients under 30 are bludgers by cutting benefits off completely for six months at a time.
With youth unemployment up to 40 per cent in some areas, these young people need support, not punishment. Pushing young adults under 24 years of age onto the cheaper Youth Allowance – cutting about $45 a week - looks like what it is: mean and nasty."
Senator Xenophon has lined up with Clive Palmer, whose Palmer United/Ricky Muir bloc of senators, will wield the most power in the new Senate, against changes to university funding.
"Lifting the cap on uni fees and doubling the interest rate for HECS repayments is just plain dumb. So much for equal access to education. With the cap on fees for uni degrees lifted, the real cost of doing a degree will skyrocket and the government should not be surprised when undergraduate numbers plummet, including for qualifications in which we have national shortages like science and engineering."
Senator Xenophon predicted a blow out in hospital costs as a result of the government's introduction of a $7 Medicare fee.
"And don't get me started on the government's Paid Parenting Scheme. It's not that PPL is a bad idea, but the priority in these times of austerity must be to make childcare more affordable so that more women can remain in the workforce. This makes the $230 million cut to child care all the more baffling and counter-productive.
"If we got the same rates of participation in the workforce for women as Canada (6 per cent higher than Australia), which has a much smarter policy on affordable child care, it would mean a $25 billion boost to our GDP."