A key cross bencher in the lower house says he will no longer guarantee supply or confidence to Malcolm Turnbull's government.
Queensland MP Bob Katter says he will not automatically support the government, effectively costing the Coalition a vital vote in the House of Representatives.
The Liberal and National Party Coalition holds just 76 of the 150 lower house seats in its own right.
"I wanted and need certain things. I wasn’t delivered certain things," Mr Katter told Sky.
He said it was now "back to the drawing" board.
Mr Katter’s declaration comes after the Turnbull government was already left hanging by a thread as it mulls the potential loss of deputy prime minister Barnaby Joyce.
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Mr Joyce’s eligibility for office will be examined by the High Court after it was revealed he held dual citizenship with New Zealand.
Under the Constitution it is illegal for a dual citizen to hold a seat in the federal parliament.
Mr Joyce is not likely to know until October or November if he will be allowed to hold on to the northern NSW seat of New England.
However, the loss of the Joyce and Katter votes would not automatically hand government to Bill Shorten's Labor. Labor holds just 69 seats in its own right and would need to convince the Governor-General it can command a majority on the floor of parliament.
Labor would need to acquire the support of the Greens, the Nick Xenophon team and independents Cathy McGowan and Andrew Wilkie, as well as gaining the support of whoever replaced Mr Joyce to control the house.