When lawyers for the federal Conservative Party and a defeated Liberal MP assemble before the Supreme Court on Tuesday, they'll be fighting over more than whether voters in one riding should head back to the polls.

At the heart of the potentially precedent-setting case – one considered important enough that the court has interrupted its summer break to hear it – is whether Canada's voting system can be trusted to function properly.

Critics warn that if the 2011 federal election results in Etobicoke Centre are thrown out, the bar could be lowered for future legal challenges of ballot outcomes, setting the stage for court battles in the years ahead as losers sue for do-overs.

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The facts are that Tory MP Ted Opitz eked out a slim victory in the Toronto-area riding of Etobicoke Centre during the 2011 general election, defeating incumbent Liberal MP Borys Wrzesnewskyj by a mere 26 votes.

But what happened behind the scenes is hotly disputed and the Supreme Court is being asked by the Liberal second-place finisher to determine whether Elections Canada fumbled the conduct of the election – and what should be done about it.

"This process is about restoring Canadians' confidence in the integrity of the Canadian electoral system," Mr. Wrzesnewskyj said.

The former MP wants the Etobicoke Centre election results tossed and a new vote held because, he says, a significant number of electors cast ballots without proper authorization.

An Ontario judge agreed with him in May, paving the way for Tuesday's confrontation at the Supreme Court.

On May 18, Ontario Superior Court Judge Thomas Lederer voided the election outcome in the riding after ruling that errors by Elections Canada staff on voting day – May 2, 2011 – meant 79 voters were improperly cleared to cast votes in Etobicoke Centre. That's more than three times Mr. Opitz's margin of victory.

Mr. Opitz, however, says to hold another ballot now would unfairly ignore the decisions of more than 50,000 people who voted 14 months ago.

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Instead of accepting the Ontario judge's decision and calling a by-election, the governing Conservatives decided to fight it, becoming the first party to take such a matter to the Supreme Court. The Tory party is paying Mr. Opitz's legal bills.

Judge Lederer's May ruling was only the sixth time since 1949 that a Canadian court has set aside federal election results in a riding.

The Supreme Court is expected to rule fairly quickly in this matter. There is a lot at stake. Mr. Opitz could be out of a job. Mr. Wrzesnewskyj, who has spent $300,000 of his own money fighting for a new election, could find himself without anything to show for it. Elections Canada calls itself a neutral observer in this case, but it's trying to introduce evidence that would apparently reduce the magnitude of the errors committed by its staff in Etobicoke Centre.

It says it has further researched the names of voters who were determined to have been improperly registered to vote in the riding – and 44 of the 79 whose ballots were set aside by the Ontario court were in fact Canadian citizens and qualified to vote.

Elections Canada is asking the Supreme Court to include this information in its deliberations, as is the Conservative Party.

"Borys Wrzesnewskyj called for an investigation into what happened in Etobicoke Centre," Conservative spokesman Fred DeLorey said. "Elections Canada [has] investigated and found that the majority of the questionable voters in Etobicoke Centre, according to Judge Lederer's decision, were in fact qualified voters."

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"This is a significant development," Mr. DeLorey said.