Changes to Senate voting rules that make it difficult for micro-parties to win seats are bound for the upper house, where crossbench senators are predicted to vent their fury.
Legislation to reduce the likelihood of micro-parties getting elected through preference deals passed the House of Representatives on Wednesday without the opposition's backing.
The bill didn't sail through the lower house, with the government moving last-minute amendments to allow for voting-night counting of Senate ballots.
Labor said the amendments proved the "farce" of the government's dirty, rushed deal with the Australian Greens.
The Greens' support all but guarantees its passage through the Senate, where crossbench senators are fuming.
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Several of the eight small-party crossbenchers believe the changes spell the end for their parties and are expected to take aim at the government in their speeches on the bill.
Prime Minister Malcolm Turnbull says the bill will end backroom preference deals between parties and put more power in the hands of voters.
But his government faces a backlash if the changes go through, with talks underway between micro-parties on standing candidates in marginal lower house coalition seats.
Glenn Druery, whose advice on preferencing has delivered a swag of seats to micro-parties, says he's been contacted by more than 20 parties.
The "fog" of having 10 to 15 micro-parties standing in a seat, with a tightly organised swap of preferences, could be enough to unseat some sitting members, he said.
The opposition failed on Wednesday to delay the Senate vote on the bill until May 12, one day after a double dissolution election could be called.
Veteran Labor frontbencher Gary Gray, who has long campaigned for Senate voting reform, admitted he had lost the debate within his party.
