Almost half of all federal political donations over the past year came from just four companies and one industry group.
The largest single donor revealed on Monday in the Australian Electoral Commission's figures was billionaire Clive Palmer's Mineralogy, which gave $5.9 million to the mining magnate's own United Australia Party.
Other big donors included Pratt Holdings ($1.55 million), Woodside Energy ($335,415), Macquarie Group ($251,230) and the Australian Hotels Association ($232,301).
All of the Pratt Holdings donations went to the National and Liberal parties, while Woodside gave to both the coalition and Labor party organisations.
The $8.3 million in donations from five organisations represented 46 per cent of the total received in 2019/20, according to an analysis by the Centre for Public Integrity.
The National Party disclosed a $75,000 donation from Mineralogy, but it was not noted in the company's disclosure.
Nationals federal director Jonathan Hawkes told AAP the Mineralogy donation was "declared as required under current legislation".
"Any questions regarding the disclosure of the amount by Mineralogy Pty Ltd are best referred to that organisation," he said.
AAP was seeking a comment from Mineralogy.
Overall, the Liberal-National coalition received $59 million in donations, compared with Labor's $50.7 million.
Professor Joo Cheong Tham, a director of the Centre for Public Integrity, said the absence of caps on political donations meant a handful of donors would dominate.
"That the most significant level of government has the weakest political finance laws is a grave weakness of Australian democracy," Prof Tham said.
The Greens are hoping to bring to parliament this month a bill which would ban donations from companies seeking approval or applying for government tenders or contracts while their application is on foot, or six months on either side of it.
Greens senator Larissa Waters said the party would rather get support for broader reform of the donations system - including real-time disclosure and a $1000 cap - but the bill would still be a small step forward.
"It's common sense," she told AAP.
"You should not be able to bribe your way into an approval or government contract."
Australian Conservation Foundation democracy campaigner Jolene Elberth said it was concerning that 32 per cent of total income declared by parties was "dark money" - having no identifiable source.
Attorney-General Christian Porter said the $5 million donated by unions over the year showed who was calling the shots in the Labor Party.
"Surely that money would have been better spent with a focus on the real and immediate needs of workers during the last year," Mr Porter said.
"At a time when union members are most in need of practical assistance, the unions still seem to be focused on business as usual - transmitting of huge amounts of membership fees to Labor politicians."
Australian Associated Press