Prime Minister Scott Morrison says it's "unlikely" the government will be able to get its income tax package through Parliament before June 30.
Tax offsets for 10 million Australians could be delayed while the government waits for the final votes to be counted, despite previously assuring taxpayers the election would not be an issue.
The payment of up to $1080 for low and medium income earners was promised in the federal budget, handed down on 2 April, and was a central plank of the government's re-election pitch.
But Prime Minister Scott Morrison has admitted its "very unlikely" he will be able to recall Parliament in time before 1 July, when workers start submitting their tax returns.
That may force the Australian Tax Office to make a retrospective payment once the income tax package passes Parliament, placing a huge bureaucratic burden on the ATO.
Mr Morrison said he hoped to convene Parliament as soon as possible.
"We obviously have to wait for the writs to be returned and there’s a formal process for that," Mr Morrison told Sky News on Monday night.
"At the moment that’s not looking until very late in the back end of June, so that really does make very narrow that opportunity to do it before the 30th of June.
"I think that's very unlikely with the advice I've received."
In the lead up to the election being called, the government dismissed Opposition concerns that there would not be enough time to enable the tax offsets to flow from 1 July.
Treasurer Josh Frydenberg assured Australians there would be "no impediment" to implementing the changes, telling The New Daily that Parliament was likely to sit for several weeks before the end of the financial year.
Labor's treasury spokesman Chris Bowen said it was a broken promise.
"The election is not even a couple of days over and Scott Morrison has broken his promise," he said.
"If Australians have to wait another year for the tax cuts, I think it's an indictment on his government and the character of the prime minister."
Senate support uncertain
The income tax package will need the support of Labor, the Greens or most crossbenchers to get through parliament.
Liberal Senator Zed Seselja is urging Labor to support the changes in order to give them a seamless course through parliament, avoiding the need for the crossbench votes.
Greens leader Richard Di Natale said the minor party won't support the income tax cuts.
The party held onto all of its six Senate seats up for re-election, taking the Green's total to nine.
"We had millions of Australians voting for parties like the Greens in the Senate to hold this government to account, and we'll do that," he told ABC radio.
"We're not going to support tax cuts to people on half a million dollars ... if any support is going to be given it needs to be targeted at people on low incomes."
Additional reporting by AAP