Nearly half a billion dollars of taxpayer cash was given to a private charity within 24 hours of it striking a deal with the Turnbull Government in June.

9NEWS has confirmed that $443.3 million dollars was paid into the account of the Great Barrier Reef Foundation on June 28, the day after it signed the grant agreement with the Department of the Environment.

The Turnbull Government is under increasing pressure to explain a controversial payment, with the Opposition demanding the cash be returned because it lacked the basic probity required for the expenditure of so much money.

Prime Minister Malcolm Turnbull will face a grilling over the $444.3 million grant given to the Great Barrier Reef Foundation. (AAP)

There are also questions about the foundation’s links to business and how a small organisation will manage such a large cash injection.

One unusual feature of the deal was that it was announced in the 2018-19 Budget but all the money changed hands in the dying days of the 2017-18 financial year.

9NEWS wrote to the Department asking when it received the money from Treasury and when it was paid out.

The Opposition is demanding an explanation from the government over the grant, which is meant to help save the reef. (AAP)

“The Government allocated the money for this grant in its May 2018-19 Budget,” a departmental spokeswoman said in a statement. “We received the money on 27 June 2018.”

“The grant agreement between the Department and the Foundation was formally executed on 27 June 2018. We paid the Great Barrier Reef Foundation $443.3 million (GST Exclusive) on 28 June 2018 representing the full value of the agreement.”

9NEWS asked if it was usual for the department to deliver six years of funding to a service provider in a single year.

Finance Minister Mathias Cormann (AAP)

“Grants are used widely across Government departments to achieve policy objectives, and involve billions of dollars each year going to the non-government sector”, the statement said “It is not uncommon for payments to be made in advance of work being undertaken.”

Finance Minister Mathias Cormann was asked if he could name any other examples of where a private charity received such a large amount of money on a single day.