Planned changes to the way Australians vote for the Senate could end up in the High Court.
Family First senator Bob Day flagged the prospect as he railed against a move that he claims signs the death warrant of micro parties.
The South Australian senator had called on the government to release legal advice that shows legislation, rushed into parliament on Monday, is not unconstitutional.
"Why risk illegitimate government, disenfranchised millions and taxpayers footing High Court legal bills, for political expediency?" he told ABC radio on Tuesday.
Under the changes, voters will be encouraged to number six boxes above the line.
Independent Glenn Lazarus fears the new system will entrench the Senate power of the government of the day, warning legislation would be rubber stamped without proper review.
"Rather than rolling up the sleeves and getting on with it, they'll just change the Senate so it suits them and they'll be able to ram through as much legislation as they want," he told ABC radio.
Special Minister of State Mathias Cormann denied the changes were designed to benefit the coalition at the ballot box.
"I don't accept that, the result of the next election is a matter for the Australian people," he told Sky News.
The Labor caucus is expected to discuss the changes when it meets in Canberra on Tuesday.
But frontbencher Chris Bowen says Labor has every right to be concerned about the measures.
"When I look at a deal between the Liberals and Greens, my alarm bells ring," he told reporters.
Liberal Democrat David Leyonhjelm believes the government is now eyeing a double-dissolution election in July.
"There is not much point implementing these changes to the voting system and then having seven cranky crossbenchers sitting there with the balance of power," he told reporter.
Senator Cormann says the Australian Electoral Commission will need three months to implement the changes once they clear parliament.
The government plans to have its legislation passed before parliament rises for the pre-budget break in mid-March.
As well as the Greens, the coalition has the backing of independent South Australian senator Nick Xenophon who used his group's experience of polling nearly two quotas at the 2013 election to argue the case for change.
"Because of a series of quite bizarre preference deals, my running mate was excluded from the final count," he said.
Based on the ACT experience, Senator Xenophon expects up to 90 per cent of Senate votes will be cast above the line if parliament approves a "better and fairer" system.
