WESFARMERS has revealed it is investigating its Coles business over claims the grocer is heavy handed in its treatment of suppliers.

Speaking as he revealed Coles' profit surged in the first half, Wesfarmers chief Richard Goyder said the investigation had been under way for "a while", the Herald Sun reports.

The revelation yesterday came after Australian Competition and Consumer Commission chairman Rod Sims said the watchdog was assessing whether Coles and Woolworths were abusing their market power.

Addressing a Senate committee on Wednesday night, Mr Sims said the ACCC was looking into allegations of "unconscionable conduct" by the major supermarket groups in their dealings with suppliers.

Mr Goyder said Wesfarmers supplied information to the commission.

"We are doing our own investigations and obviously the Australian Competition and Consumer Commission is doing its and we will just let it all unfold," he said.

He challenged Mr Sims' suggestion Australia needed an enforceable code of conduct for supermarkets in their dealings with suppliers.

"What I don't support is bureaucracy," he said.

Accounts reveal Coles' earnings before interest and tax soared to $755 million in the six months to December - up 15.1 per cent on the same period a year earlier.

Across the group, net profit jumped 9.3 per cent to $1.285 billion in the first half, while revenue climbed to $30.6 billion.

The company said strong earnings growth at Coles, Bunnings and Kmart - along with a turnaround in the insurance division - "more than offset" a 20.4 per cent fall in earnings at Target and in the resources division.

Wesfarmers declared a fully-franked interim dividend of 77c a share.

The group's shares closed 1.2 per cent higher at $38.88.

Read more at the Herald Sun.