The competition regulator is looking into claims the supermarket giants improperly forced down the prices they pay suppliers.
Around 50 suppliers are believed to have come forward with complaints.
The ACCC says, if proven, the more serious allegations carry multi-million dollar fines.
"I then promised confidentiality to suppliers and said we'd do all we can to keep what they say confidential," he explained.
"We eventually had around 50 come forward, and I suppose it's fair to say we've got some fairly credible and consistent issues that we now believe we need to investigate in some detail."
The company's CEO Richard Goyder says Wesfarmers wants to do the right thing.
"We'll cooperate fully with the ACCC on any investigation they may undertake," he said.
"In the meantime we're doubly insuring that we've got the right processes in place to deal with our suppliers - our suppliers have been significant winners from the turnaround in Coles over the last five years."
Between them Coles and Woolworths control about 70 per cent of the nation's grocery market.