Labor is renewing calls to overhaul political donation laws after the latest financial disclosures were revealed.
Political parties received more than $168 million in the last financial year, with one particular contribution sparking fresh calls for change.
Mining magnate and former federal politician Clive Palmer donated $75,000 to the Nationals, as well as nearly $6 million to his own party.
While the Nationals disclosed the donation, his company Mineralogy did not.
However, Mr Palmer - who also spent more than $60 million on advertising during the 2019 federal election campaign - said on Tuesday the company's disclosure would be amended to fix the "administrative staff oversight".
Labor frontbencher Don Farrell said the contributions showed why the system was broken.
"You cannot have a situation where Clive Palmer is funding both his own political party and the coalition. It's just unacceptable," he told ABC radio.
"What we want to see is public disclosure about the donations and to set a limit on how much organisations and individuals can donate."
Nationals deputy leader David Littleproud defended the existing arrangements, which allow individuals and organisations to donate as much as they want to as many political parties as they choose.
"Individuals, last time I looked in Australia, were free to do what they liked within the confines of the law," Mr Littleproud said.
Currently, political parties are only required to disclose donations above $14,000 and Labor wants the threshold dropped to $1000.
Tasmanian independent senator Jacqui Lambie is concerned about donations from unknown origins.
"If this money is not buying influence, what are they so scared about putting those donations down on paper for and doing it in real-time disclosure?" she said.
"Seriously, if they're not buying influence, what is stopping them?"
Mr Littleproud is open to a discussion on donation transparency laws.
"We shouldn't be afraid to have mature conversations about political funding into the future," he said.
"I'm comfortable with having those conversations, we should."
Almost half of the $18 million in political donations over the past year came from just four companies and one industry group.
The largest single donor in the Australian Electoral Commission's figures was Mr Palmer's mining company Mineralogy, which gave $5.9 million to his 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 Greens are hoping to bring to parliament 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.
