A push is on to take a 0.05 per cent tax from big financial transactions instead of levying GST across the board.

The NSW Public Sector Union has joined with the state’s Nurses Union to deliver an intriguing request to world leaders at the G-20 summit in Brisbane this weekend.

Two of the state’s largest unions want to talk about a ‘Robin Hood’ tax to help the disenfranchised.

It would likely consist of a small tax on financial transactions, like trades in derivatives and hedge-funds.

The idea being that taking a small slice of high-money deals is fairer than the GST.

The unions’ reasoning says that the GST is fixed for all people, regardless of income, but a ‘Robin Hood’ system would not disadvantage those already struggling.

“A financial transactions tax is a tiny tax on the huge profits the banks are making,” Nurses Union rep Michael Whaites has told the ABC.

“We're talking 5 cents in every 100 dollars on the trade in derivatives and hedge-funds.

“The sort of high-volume trades that bankers and finance marketeers are making every second of every day.

“So we're looking at taxing a tiny amount on the profits and transactions they make.”