Senior federal government minister Mathias Cormann insists he is comfortable with a half-billion dollar grant handed to a small Great Barrier Reef charity.
The Turnbull government gave $444 million in taxpayer funds to the Great Barrier Reef Foundation earlier this year, without a competitive tender process.
The foundation has just six full-time staff and there is no clear plan so far for how the money will be spent.
"Of course it is a very significant investment into the future health of the Great Barrier Reef," Senator Cormann told ABC radio on Monday.
"This is something that the parliament, including of course the Labor party, has voted in support of."
Opposition MPs have been piling pressure on the government over what Labor calls a "curious" decision.
"This deal, from beginning to end, has been an inappropriate and dodgy use of taxpayer money," Labor environment spokesman Tony Burke told the ABC.
"Every question that gets asked about this, the more the government answers them, the more dodgy the whole process becomes."
Mr Burke is concerned the decision means CSIRO reef scientists might have to go through the foundation instead of the government for funding and normal methods of ministerial oversight will be undone.
Environment Minister Josh Frydenberg has argued there's nothing unusual about the grant.
The funding was contained in a budget submission Mr Frydenberg brought to cabinet, although he has declined to specify whether or not it was his idea.
"This was not an idea developed overnight," he said on Sunday.
"It goes back to early last year when my department chaired an inter-departmental task force looking at how we meet the challenges from the reef."
Mr Frydenberg would not be drawn on what exact steps were taken to ensure the foundation was the best candidate but added "there was extensive due diligence".
The grant was made to the foundation, a charity set up in 1999 following the first mass coral bleaching 20 years ago, as a single lump sum.
"It is not unusual for governments to do that," Mr Frydenberg said.
"The money is to be spent over six years. By giving it all at once, they have maximum leverage to enter into contracts and start providing the money as needed, as they meet their objective."
Labor has called for the grant to be handed back.
The foundation's partners comprise businesses like Qantas and BHP and institutions such as ANU and the federal government's Great Barrier Reef Marine Park Authority.