Elections Canada has launched a formal investigation into complaints by various Liberal candidates in Ontario that someone is making repeated phone calls to voters, purporting to be Liberal supporters — often at odd hours, including the middle of the night.

The Liberal Party is blaming rival operatives for setting up the harassing, late-night phone calls that ask residents to vote Liberal. The calls seem to be targetting ridings expecting close races.

A CBC News investigation has been chasing down numerous complaints from local Liberal campaign offices across Ontario, including Oakville, St. Catharines, Haldimand-Norfolk, Simcoe Grey, Guelph, Eglinton-Lawrence, St. Paul's and Mississauga East-Cooksville. The calls have also happened in Egmont, P.E.I., and St. Boniface, Man. CBC News has not been able to determine who is making the calls.

Have you had calls? If you have a news tip about the phone calls, email dave.seglins@cbc.ca

Bob Rae, the Liberal candidate in Toronto-Centre, told reporters Tuesday morning the calls must be coming from another party.

"If you want to get support for your party, it's not a very good idea to phone people at 2 a.m.," Rae said in Ottawa. "I think everybody understands that. So it's likely to have come from some other party."

Steve MacKinnon, who's running for the party in Gatineau, Que., went further, suggesting the Conservative Party is responsible.

"I haven't experienced anything like that, but it might have a lot to do with the fact that the Conservatives aren't particularly present in the riding of Gatineau," MacKinnon said.

But Conservative spokesman Alykhan Velshi said the party isn't involved, "period."

"The only party with access to the Liberal Party member list is the Liberal Party. Are you certain they aren't making the calls to their members?" he said.

The call targets are not limited to Liberal Party members, however. CBC News' Dave Seglins has spoken to NDP and Conservative supporters who also got bombarded with calls.

The Liberals have looked into whether it's their own people who are making the calls, says John Mraz, an adviser to the party.

"What they're essentially doing is accusing us of incompetence," Mraz said.

"I find it impossible to believe that campaigns would be unaware of recordings that have been manipulated with their candidates' voices that are being autoblasted out three, four, five times in an evening. We can find no forensic evidence anywhere that any of our service providers have made those calls. And we have checked."

Liberal candidate Bob Speller has said the calls in his Haldimand-Norfolk riding use his voice.

Tactic used in U.S.

Mraz said the calls have been used in the U.S. to suppress the vote. The technique involves angering voters so much they stay home on election day.

"It's absolutely clear to me that my party is not engaged in voter suppression tactics of any sort," Mraz said. "And certainly it's clear to me that we would never repetitively call our supporters or our identified Liberal voters in the middle of the night, four times in an evening, on a Sabbath when we know them to be practising their faith. These calls are very clearly being organized by someone with the intent of suppressing Liberal vote."

Ronald G. Shaiko, senior fellow at Rockefeller Center at Dartmouth College in New Hampshire, says both Democrats and Republicans have both tried the strategy, but it's usually associated with Republicans because lower turn-out tends to benefit that party.

Shaiko says it's likely a third party is responsible for the calls.

"I assume, like the American parties, that there are shadow organizations that are directly aligned with both the Conservatives and the Liberals and that with a straight face the leaders of the two parties could say 'we have noting to do with this'," Shaiko said.

CBC has also contacted most of the Conservative, NDP and Green Party candidates in the ridings reporting the calls, and none of them have had reports of harassing calls from people who say they represent their parties.

Calls at Passover celebration

Among the most recent complaints are some coming from residents in the Toronto riding of St. Paul's, where Jewish voters complained about receiving harassing calls during last night's Passover celebrations. Liberal candidate Carolyn Bennett vehemently denies her campaign made any such calls and tweeted Tuesday: "Not us. Play fair!"

Liberal candidate Joe Volpe said in a news release Tuesday that his riding was also targeted during the Sabbath.

"Only our political opponents would benefit from these incessant phone calls, a tactic taken straight from the Republican dirty-tricks playbook," Volpe, a candidate in Eglinton-Lawrence, said in the release.

Speller complained on Friday to Elections Canada that someone is purposely sending out repeated automated calls with a recording of his voice on it, and with a call display showing the same local-area-code number.

The CBC has spoken to dozens of people who reported the rude or repeated automated calls, as well as Call First, the company contracted by the Liberals to do legitimate automated calling. Owner Mike O'Neill said he believes someone may be "spoofing," or faking, the caller ID to show a number the Liberals have used in the past for a telephone town hall.

And he suggested someone has used a recording of Speller's voice to fabricate unauthorized automated messages, insisting the calls eliciting complaints are occurring during days and hours when neither his company nor the Liberals have made any calls. CBC has been unable to confirm the true origin of the 519-area calls.

CBC has also received complaints from residents from Eglinton-Lawrence, Simcoe-Grey and Sudbury claiming that they are getting repeated calls from a North Dakota area code, with either rude live callers or automated messages purporting to be from Liberals.

The Liberals insist they are not behind the calls and have not hired any U.S. company. The number traces to a cellphone number in North Dakota, and a message at the other end says it is a call centre. CBC has not been able to confirm who is behind the calls, the number, or whether the number is simply a "spoofed" caller ID.

'It's absolutely disgusting'

Raymond Simard, the Liberal candidate in St. Boniface, says his campaign first heard about the calls Monday and is looking into it.

"We were door-knocking in some of our buildings, and people had just indicated that we were calling them at the same time," he said. "We said absolutely not. So it is happening, they're calling our offices saying people are being rude with them."

Simard says he asked other candidates about it on a conference call and they believe it's happening in nine ridings.

"Something is going on," he said. "They are targeting ridings they think are vulnerable. It's an organized scam, trying to irritate voters. It's absolutely disgusting."

The campaign is starting to look messy, with signs being defaced and a Liberal supporter charged with stealing a Conservative competitor's signs in Brampton-West, just outside of Toronto. Rachpal Singh Grewal, who says the signs found in his car were planted, has a court date in May.