Whistleblower lifts the lid on Coles, Woolworths price gouging tactics

The bosses of Australia's biggest supermarkets are bound for Canberra, set to appear before a Senate committee.

Unions, farmers and the consumer watchdog spoke about the squeeze being felt across the country as whistleblower Abdel Badura blamed the grocery giants.

"Blowing the whistle on the supermarket duopoly is the biggest risk I have taken both personally and professionally," Badura said.

Badura spoke out as the Senate examines supermarket pricing, calling on his experience working for suppliers dealing with the big grocers, which will have their say tomorrow.

"During this time I have witnessed the tactics and practices Australia's supermarket duopoly Coles and Woolworths deploy to price gouge suppliers and ultimately customers," Badura said.

Greens Senator Nick McKim said these two days "are going to be critical for this inquiry".

"Ultimately the CEOs of Coles and Woolworths are going to need to explain," McKim said.

A review of the grocery code of conduct is under way.

Coles and Woolworths support making the voluntary code mandatory.

The interim review has already suggested billions of dollars in fines if sustained price gouging is found.

"Where a matter is brought to us that incorporates significant harm and systemic harm occurring, then we take action," Australian Competition and Consumer Commission deputy chair Nick Keogh said.

This is one of six inquiries currently looking at supermarkets.

The majority of senators have called for so-called divestiture powers that could force the big supermarkets to sell if the businesses are found to be abusing their market share.

"The biggest recent divestiture was AT&T in the US and that's had a massive positive effect on jobs," former ACCC boss Allan Fels said.

Prime Minister Anthony Albanese is against the move as he is worried about the impact on competition.