A Labor senator does not see how it is feasible for the Senate to pass the May budget's money bills and debate a crucial piece of legislation in time to trigger a July 2 double dissolution election.
The Turnbull government has left open the option for an early election but that would need to be called on May 11, the day after the budget is due to be delivered.
The government could use the Australian Building and Construction Commission legislation as an election trigger should it fail to pass the Senate for a second time.
Labor senator Sam Dastyari says no one has explained to him how all that is possible in the time that has been allotted with the upper house not due to return until May 10.
"I can't see how this is feasible," he told Sky News on Sunday.
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But he reassured the government that Labor would pass the budget's appropriation or money bills.
Greens Leader Richard Di Natale believes if the Turnbull government is able to rush to a double dissolution election it will look like a sign of panic.
He says it would be a mistake, particularly with the coalition's tax reform agenda in tatters.
"The government does look very divided, it looks shambolic at the moment, and to sort of be panicking and running to an early election ... I don't think it would a good look for them," he told Sky News.
Senior Liberal Arthur Sinodinos said if the Senate passed government legislation, there would be no need to contemplate early election options.
"Yet something which is a major promise we put up in lights in the last campaign, we can't implement in this parliament," he told ABC television.
That was why the government wanted the Senate voting reforms, which were passed last week, he said.
Family First senator Bob Day and Liberal Democrats senator David Leyonhjelm, who face being booted out at a possible double dissolution election under the new voting rules, are mounting a High Court challenge to this legislation.
"It's their right to do that - I suspect it will fail," said Senator Di Natale, who supported the changes.
