The former Australian prime minister Kevin Rudd has launched a petition calling for a royal commission into NewsCorp’s dominance of Australia media, arguing Rupert Murdoch’s media company employs tactics that “chill free speech and undermine public debate”. The petition, launched on the Australian Parliament website on Saturday, had gained more than 38,000 signatures by Sunday morning, with Rudd tweeting that the popularity of the petition had caused the website to suspect users signing it were robots. While the petition calls for a royal commission “to ensure a strong, diverse Australian news media” in the face of “new business models that encourage deliberately polarising and politically manipulated news”, Rudd posted a video to Twitter launching the petition that focused on “growing anger at what the Murdoch media monopoly is doing to our country”. However it is unlikely the petition will be acted on by the federal government because Australia – unlike other governments, including the UK – has no threshold of signatures that requires a petition to be debated in parliament. Explaining how he arrived at his current view of the media empire – which includes the Australian and several newspapers that endorsed him at the 2007 federal election – Rudd said the company’s mastheads had become an “arrogant cancer” on the country’s democracy. “The truth is Murdoch has become a cancer, an arrogant cancer, on our democracy,” Rudd said. He said 70% of Australia’s print readership was owned by Murdoch and he owned virtually every newspaper in Queensland “which swings so many federal election outcomes”. Over the past decade, in 18 out of 18 federal and state elections, “Murdoch has viciously campaigned in support of one side of politics, the Liberal National party, and viciously campaigned against the Australian Labor party,” Rudd said. “There’s no such thing as a level playing field any more.” Rudd said Murdoch retained loss-making newspapers in Australia to maximise his political power in defence of climate change denial, and pursue his commercial interests in relation to the national broadband network. “The final reason we need this royal commission is the sheer arrogance and swagger and bullying behaviour by Murdoch and his editors against anybody who stands up against him or has a different point of view.” Guardian Australia contacted the Australian parliament to clarify the cause of issues on its petition website.