Malcolm Turnbull has come out swinging over his $1.75 million donation to the Liberal party, saying opposition leader Bill Shorten is "owned" by the unions which prop up Labor.
The opposition accused the prime minister of buying himself an election after he revealed on Wednesday night he had made the generous donation during last year's campaign.
But Mr Turnbull hit back at Labor and Mr Shorten, saying his donation is a world away from being "owned" by a union.
"Let's be quite clear about this - I have put my money where my mouth is," Mr Turnbull told reporters in Melbourne on Thursday.
"I can't be bought by anyone. I'm not a wholly-owned subsidiary of the CFMEU (construction union) like Bill Shorten. I'm my own man and Bill Shorten hates that."
Mr Turnbull said Labor, the unions and GetUp had "massively out-spent" the coalition during the election campaign.
"They had a big financial advantage," he said.
Opposition finance spokesman Jim Chalmers said Mr Turnbull had to buy his way out of trouble.
"If Malcolm Turnbull didn't have $1.75 million to splash about he wouldn't be the leader of the Liberal Party and he wouldn't be the prime minister," he told ABC radio on Thursday.
Mr Shorten said the public would determine whether Mr Turnbull's donation was appropriate.
But he said it was time to overhaul the donations system, including moving public disclosure closer to when donations were made and a ban on foreign money.
Deputy Labor leader Tanya Plibersek defended union donations to the ALP.
"Unions are made up of individual people who put their hard-earned dues into the movement. They have a democratic say about the leadership of their union movement," Ms Plibersek told the ABC.
"Their own interests are represented by the union movement that fights for better pay and conditions for working Australians and fights for services too, like decent healthcare, better education, more money for schools, universities and hospitals."
Treasurer Scott Morrison said Mr Turnbull and his wife Lucy were generous and humble contributors to many great causes.
"That's a grubby political smear from a grubby political hack in a party of hacks led by Bill Shorten," he said of Mr Chalmers' attack.
Crossbench senator Nick Xenophon argues both major parties were as bad as each other when it comes to political donations.
"People in glass houses shouldn't throw stones and this is one hell of a big glass house," he said.
Senator Xenophon believes there needs to be real-time disclosure of donations to overcome a lack of transparency.
Mr Turnbull told the National Press Club on Wednesday he backed a ban on foreign donations and favoured more timely declarations of political donations, but would await a report by a parliamentary committee before changing the law.
He made his donation in the current financial year, which was why it was not disclosed in Australian Electoral Commission figures for 2015/16.