Supporters of Stephen Harper have formed a political-advertising unit separate from the Conservative Party that will run attack ads, targeting Facebook, Google and Twitter users, to help the Tory re-election effort as a federal ballot approaches.

HarperPAC has already produced a spot alleging Liberal Leader Justin Trudeau is unqualified to be prime minister and its next project is an ad, aimed at British Columbia voters, that will warn against electing a federal NDP government.

Spokesman Stephen Taylor said HarperPAC doesn't take direction from Conservative Party national campaign manager Jenni Byrne but it has chosen on its own to focus on B.C., where polls suggest NDP fortunes are rising.

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HarperPAC is composed largely of former Harper government staffers who want to give him a helping hand in the growing battle for the hearts and minds of Canadian voters. PAC stands for "political action committee," a phrase more common in the United States, where third-party interests play a bigger role in election campaigns.

This group represents a broadening of spending on the Conservative re-election effort and yet is not constrained by the need to discuss serious matters the way the official Harper campaign is. "We can be pure politics. We don't have to talk about tax policy or child policy," said one HarperPAC adviser who spoke on background because the adviser wasn't designated to speak to the media.

Mr. Taylor declined to reveal donors to his group, saying only that they are Canadian citizens and Canadian businesses.

He says HarperPAC is a reaction to efforts by unions and other centre-left interests to mount an anti-Harper ad campaign. He singled out Engage Canada, run by a number of Liberal and NDP backroom veterans, which has already bankrolled political advertising aimed at defeating the Conservatives.

Mr. Taylor's group wants to blunt the impact of left-of-centre advertising on Mr. Harper. He notes that during Ontario's 2014 election campaign, the Working Families Coalition of unions, which opposed the election of the province's Progressive Conservative Party, spent more than $2-million on ads.

"We're messaging on conservative principles and values in response to what the left is doing to attack the very same."

HarperPAC's emergence means the Tories can benefit from more spending on advertising both before the writ is dropped and during the election campaign, expected to begin in late August or early September, when expenditure limits come into effect for political parties.

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The target audience for these pro-Harper campaigners is swing voters who may have drifted away from the Conservatives or remain merely lukewarm supporters of the party that has governed Canada for more than nine years.

The advisory council for HarperPAC includes Kasra Nejatian, former director of strategic planning for Jason Kenney when he was immigration minister, Michelle Austin, former chief of staff to Maxime Bernier when he was industry minister and Chris Froggatt, former chief of staff to John Baird when he was transport minister.