TWO independents have teamed up to force the major supermarket chains to reveal how much they pay farmers for fresh produce.

Senator Nick Xenophon and Bob Katter will introduce legislation in both houses of parliament to force supermarkets to display the price they pay at the farmgate alongside the retail price of fruit and veg.

The pair have set up their own fruit and veg stand outside a Woolworths store in Adelaide's Rundle Mall today to back their argument that both farmers and consumers are being ripped off.

"We need to have paddock to plate price transparency," Senator Xenophon said.

"Right now farmers are being paid a pittance for their produce while shoppers pay a small fortune for their groceries."

Mr Katter said Australia currently had the lowest paid farmers in the world.

"So the cheapest food in the world is produced by Australian farmers," he said.

"But consumers get no benefit because there are only two people in the market place."

"Coles and Woolworths have between 88 and 92 per cent of the market.

"So they'd be stupid if they didn't put these colossal mark-ups on.

"But you won't find those colossal mark-ups anywhere else in the world and it's got to stop."

Senator Xenophon said he believed the transparency measures would result in both farmers being paid more and consumers paying less.

"It means Coles and Woolworths would need to justify their enormous mark-ups," he said.

"That's the real issue here, farmers are getting a raw deal."

The MPs expect to get strong support for their proposal from other independents in parliament and the Greens.