The Coalition has launched blitzes of negative ads about One Nation ahead of the Farrer byelection, with the Liberals setting up a Facebook page and website accusing the populist right-wing party of having “no solutions” and an atmosphere of “chaos” in their candidate selection.

The ads, carrying an authorisation from the Liberal party, are also heavily critical of Pauline Hanson’s decision to employ convicted rapist Sean Black to work in One Nation’s headquarters until this month.

It is the latest iteration of a growing trend in Australian politics, where campaigners create social media pages with different names and imagery without obvious party branding, to promote negative ads against their opponents. The Liberals have also reactivated a page from the 2025 election, called “Teals Revealed”, to scrutinise the Climate 200-backed candidate, Michelle Milthorpe.

The 9 May byelection, precipitated by the resignation of former Liberal leader Sussan Ley, is being contested by a crowded field including the Liberals, Nationals, One Nation and Milthorpe. A March poll, commissioned by The Australia Institute, found 29% of Farrer voters said they would back One Nation, 23% would support Milthorpe, and 19% for the Liberals. Former Nationals leader David Littleproud has suggested his party could run last.

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Losing Farrer – which has been held by the Liberals or Nationals since its creation in 1949 – to Milthorpe or One Nation’s David Farley could be a blow to the new Liberal leader, Angus Taylor, that will reduce the opposition’s meagre parliamentary numbers.

It comes as Liberals and Nationals will preference One Nation ahead of Milthorpe in the poll – in a potential blow to the independent’s hopes of winning the seat.

The Liberals have already spent at least $1,600 on targeted ads for a new Facebook page called “One Nation. No Solutions”. The ads are being promoted across Facebook and Instagram, with authorisation from Liberal campaign director Andrew Hirst, but only started running on 15 April. This reflects a recent shift to a more aggressive stance against One Nation from the conservative major parties.

Party sources said the major parties were working out how best to campaign against the insurgent One Nation threat. A Liberal source said that such ads may not budge “rusted-on” One Nation backers, but could affect “soft” supporters who have recently switched their vote.

The page has promoted ads that say: “One Nation have an appalling record with candidates and employees. Are One Nation worth the risk?”, while several other ads criticise Black’s recent employment.

Black, who in 2018 was jailed for rape and subsequently lost his appeal against the conviction, was initially rehired by One Nation in 2020 as a campaign director after serving his time. He remained employed by the party until last week, when Hanson said she sacked him, but both Hanson and former Nationals MP Barnaby Joyce subsequently defended the party’s decision to hire him; Hanson said he “did his time” and Joyce suggested convicted criminals needed a chance at “redemption”.

At least three types of ads – some of which include headlines from The Australian and the ABC about Black’s employment – are being promoted by the page. “Why would One Nation re-hire a convicted rapist to run its national campaign? With One Nation, do you know what you’re getting? Is it worth the risk?” the ads read.

In total, the ads have been seen up to 170,000 times across Facebook and Instagram.

Pauline Hanson’s One Nation is being targeted by the Coalition in a negative ads blitz ahead of the Farrer byelection. Photograph: Mick Tsikas/AAP

An accompanying website for the Liberal campaign points out that numerous One Nation elected MPs have quit the party “in dramatic fashion”, including “defected, expelled, resigned or disqualified”.

The Nationals have also begun running ads critical of Black on their main Facebook page.

“There’s no place in Australian politics for anybody convicted of violent sexual assault. This isn’t about second chances, this is about judgment and character,” one ad reads, telling voters that One Nation is “not what you think”. Those ads, launched on Monday, have been seen about 100,000 times.

Hanson’s office was contacted for comment. It’s understood One Nation is not concerned about the negative campaign, with senior party sources believing similar negative campaigning backfired during the South Australian election.

Milthorpe, who does not accept the teal label, is also being criticised in a series of ads from the “Teals Revealed” page, which claim she was “funded by Climate 200, just like the other Teals. Teal independents vote mostly with the Greens.”

Guardian Australia has catalogued this campaigning trend across recent elections, which allows parties to stay clearer of negative messages on their main pages, and for campaigners to focus negative messages on voters’ news feeds without the party affiliation being immediately obvious.

Joyce this week said coverage of the Black story helped lead to a dip in One Nation’s support in opinion polls, slipping from a primary vote of 26% to 24% between March and April in both the Newspoll and the Resolve poll.

“I look at polls and I suppose that there’s a little bit of bad press, especially around one of our former staffers, and I understand that,” Joyce told Sky News on Monday.