Automated phone calls were used to try to misdirect voters in the 2011 federal election, but the impact was minimal and the election of six Conservative MPs won't be overturned, a federal justice has ruled.

Thursday's ruling dismissed an application made by the Council of Canadians concerning the results in six ridings. The ruling cleared Prime Minister Stephen Harper's Conservative Party, its candidates and two phone marketing firms of wrongdoing in the so-called robo-call controversy.

However, "fraud" did occur – particularly in Guelph, Ont. – and targeted people who had previously expressed an interest in voting for anyone but the Conservatives, Justice Richard G. Mosley wrote in his ruling. But there was little evidence the robo-call efforts actually kept anyone away from the polls or that the robo-calls had any "major impact on the credibility of the vote," he ruled.

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The source of the robo-calls was "likely" a Conservative database, accessed by a person unknown to the court, he ruled. But the calls' impacts were "thinly scattered" outside of Guelph, and "the scale of the fraud has to be kept in perspective," the justice wrote.

"Had I found that any of the successful electoral candidates or their agents were implicated in any way in the fraudulent activity, I would not have hesitated to exercise my discretion to annul the result," the justice wrote. "... No such evidence was led."

The calls nonetheless struck at the integrity of the electoral process by attempting to dissuade voters from casting ballots for their preferred candidates," the justice wrote, saying such a form of voter suppression was "largely unknown in this country" until 2011.

Both sides saw good news in the case. The Council of Canadians said it was considering an appeal to the Supreme Court, noting a "judge found that the election was marred by widespread fraudulent activities."

"In a sense, it really is an indictment of the Conservative Party... it was their database," executive director Garry Neil said in an interview.

"Taken as a whole, this is a significant decision that we think is very profound."

Conservative Party spokesman Fred DeLorey noted his party's six candidates were cleared of wrongdoing. The case was "a transparent attempt to overturn certified election results simply because this activist group didn't like them," he said in an e-mail.

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The justice noted Mr. Harper's party "made little effort to assist with the investigation" and "the record indicates that the stance taken by the respondent [Conservative] MPs from the outset was to block these proceedings by any means."

It was one of two robo-call decisions revealed Thursday. The Canadian Radio-television Telecommunications Commission fined Alberta's Wildrose Party $90,000 for calls made in 2011 and 2012, because the party didn't properly identify itself.

Wildrose co-operated and paid the fine, but urged the CRTC to investigate Alison Redford's Progressive Conservatives for similar tactics.

The investigations was revealed by Global News and later confirmed by the party.

RackNine, one of the firms cleared by the federal justice's ruling, also made the Wildrose calls.