Entrepreneur Dick Smith has launched a stinging attack on News Corp and Kim Williams, the head of its local operations, News Ltd, branding the media organisation's campaign against proposed media reforms as hypocritical.

Mr Smith said News Ltd's claim that proposed media regulations would curtail freedom of speech was "claptrap" because his papers and organisation regularly censored any criticism of it. Acknowledging that he risked incurring the wrath of News proprietor Rupert Murdoch, Mr Smith went on to attack its corporate culture, and its unwillingness to tackle issues such as anthropomorphic climate change.

In the past month, Mr Williams has launched a campaign to prevent any further regulation of the media, stating that he was prepared to go to the High Court to stop the introduction of more laws.

In the letter, Mr Smith, who is a vocal supporter of the need to act on climate change, said that it was in News's commercial interests to oppose the idea that people were responsible for the rise in global temperatures.

"And I'm on to you. When friends ask me why your organisation runs such opposing views on climate change – from Fox News's claims that it's all bunkum to The Australian newspaper occasionally claiming it's accepted science - I am able to say: 'It's simple,'" he writes.

"It's all about making more money. They have worked out they will get more advertising and make more money on Fox News if climate change is debunked using sensationalism while they are likely to get greater circulation and more advertising dollars if The Australian shows a different view, so staff are directed accordingly."

In the letter Mr Smith also claims Mr Williams was personally getting involved in rejecting one of Mr Smith's ads because it mentioned the Murdoch press. In April Mr Smith said that he tried to book an ad in Sydney's Daily Telegraph to promote his Wilberforce Awards - which reward young people with leadership qualities. The ad also offered a $5000 reward to any journalist who could get the issue of climate change and finite resources covered in one of Mr Williams's papers.

Mr Smith said he found most journalists at News to be professional and fair-minded but that they censored themselves to please their boss.

He went on to say that he would normally write this kind of letter to Mr Murdoch but that the two were no longer communicating after Mr Smith criticised The Daily Telegraph for its front page attack last year on the actress Cate Blanchett after she appeared in ads supporting the carbon tax.

"Isn't it amazing – Rupert Murdoch tells people: 'Climate change poses clear catastrophic risks' and claims he made News Ltd carbon-neutral and he is treated like a hero by you and your colleagues, whereas Cate Blanchett is attacked so more papers could be sold and more profits made!" he wrote, before adding that he had been warned that releasing the letter publicly was a "high-risk strategy" and that retribution would be "swift".

"I wonder if you will instruct your reporters to come after me, just as News Ltd did to its critics in the United Kingdom? But I think it is time to stand up to your bias and bullying and put your claims of 'freedom of speech' to the test."

A response from News is being sought.