Conservatives were on defensive Monday after a report surfaced that found Elections Canada confronted the party three days before the last federal election about a potential phone scam misdirecting voters to wrong polls.
Conservatives have long said that complaints about the so-called "robocalls" began after the election.
The report also revealed those calls occurred not just in Guelph, Ont., where the story originated.
NDP MP Charlie Angus called it "the largest case of voter suppression in our country's history" and opposition MPs demanded answers.
"Elections Canada was so concerned about voter fraud it believed the Conservative party was running a scam," Angus said during question period. "Now that we have a direct link between the Conservative party and illegal voter suppression, what steps will it take to ... come clean?"
Tory MP Pierre Poilievre said the government is working "proactively" with Elections Canada "to ascertain what exactly happened in Guelph."
"We ran a clean and ethical campaign," he said.
Fred DeLorey, Conservative party spokesman, said the only calls the party made ahead of election day were to "get out the vote."
"This was all done to ensure we got our vote out," DeLorey said. "No one on behalf of the national campaign ever told anyone that a poll had changed locations."
The Council of Canadians has established a fraud hotline for voters ahead of three federal byelections.
"The service is not a substitute for Elections Canada," it said in a release. "But reports to Elections Canada are private, leaving the public in the dark about the nature or extent of complaints."