On March 24 at a business dinner in Shanghai, Forrest was reported as saying he'd be happy to cap FMG's production at 180 million tonnes to help the waning iron ore price.

He said that if the majors BHP Billiton, Rio Tinto and Vale capped their production, the price would go straight back up.

"I'm happy to put that challenge out there - let's cap our production right here and start acting like grown-ups," Forrest was quoted as saying.

Those comments prompted an investigation by the ACCC due to concerns that they could be interpreted as an attempt by Forrest to induce competitors to cap production, in contravention of the cartel conduct provisions of the Competition and Consumer Act 2010.

But ACCC chairman Rod Sims said today the commission would not take further action against Forrest.

"In deciding not to take further action on the comments that have been made, the ACCC has taken into account Fortescue's position that Mr Forrest's comments were made ‘off-the-cuff' in response to audience questions, were hypothetical and intended to encourage a policy debate about the long-term future of the iron ore industry," he said.

"However, it is important that the business community understands that public statements calling for competitors to agree to limit production or to raise prices may constitute a serious cartel offence."

The ACCC said it did not generally comment on investigations but thought it necessary to do so given the public nature of Forrest's comments.

FMG backed the comments from its chairman.

And Forrest found an ally in outspoken Cliffs Natural Resources CEO Lourenco Goncalves, who also called on the ACCC to investigate the behaviour of the majors.

"I believe that what they are doing is on purpose, and I believe that what they are doing is not right," he said overnight.

"And I believe that they are generating a lot of unemployment in Australia, and that should have serious consequence for the years to come."

Meanwhile, Forrest continued his attack against the majors yesterday on Alan Jones' talkback radio program, with Jones calling BHP and Rio "bully boys" and the Woolworths and Coles of the mining sector.

Forrest called for responsibility by the majors.

"There is a mad-cap economic theory that says you can drive everyone else out of business and be the last man standing, then perhaps you'll have a very good business," he said.

"It's all completely avoidable. None of this had to happen."

Forrest went one step further, inviting Rio chairman Jan du Plessis and BHP chairman Jac Nasser to appear on Jones' show.