The Australian Greens are concerned that John Singleton and his long-time friend Gina Rinehart are teaming up to push for a significant say in Fairfax Media.
Mr Singleton and his partner, the venture capitalist Mark Carnegie, announced late on Friday that their Gutenberg Investments had purchased a stake in Fairfax and would align with fellow shareholder, Gina Rinehart.
However, Greens Acting Leader Adam Bandt said Mr Singleton's move was cause for concern.
"I'm very, very worried that up until now Gina Rinehart has been unwilling to sign on to some very basic principles of journalistic independence and if she's now joining forces with other Australian millionaires in an attempt to set the Australian media in a different direction, I think it's of great cause for concern," Mr Bandt told reporters in Melbourne.
"I don't want to wake up every morning and find that my newspaper choice is between Rupert Murdoch and Gina Rinehart.
"I think that will be a bad state of affairs for Australian democracy."
Mr Singleton said in a statement late on Friday that he had already met with Ms Rinehart, but discussions are at a "very early stage".
"It was clear to me from the start that there was a mutual interest in working together," he said.
"However it is important to state that both Gina and I believe that the lifeblood of Fairfax is the integrity and accuracy of its journalism.
"This in no way would be compromised if Hancock Prospecting and Gutenberg Investments had a significant say in the future of Fairfax."
But Mr Singleton said the Fairfax Charter of Independence should be reviewed.
"I was on the board of Fairfax when Sir Zelman Cowen was chairman of the board some 20 years ago, when the existing Fairfax Charter of Independence was drawn," he said.
"There is no reason why a group of eminent and experienced Australians should not review the charter to ensure and enable its relevance for today, and the current very challenging times for the media."
He also took a swipe at the board and its effectiveness.
"I think the current board has struggled to come to terms with the new environment, which is there for all to see in the share price and the lack of direction at the company," he said.
Mr Singleton's decision to buy into Fairfax followed the board's decision to "definitively closing the door" on a sale or joint venture of their radio assets to his Macquarie Radio Network.