The Supreme Court of Canada is interrupting its summer break to decide whether a by-election is required in a federal Toronto riding where nearly 80 voters were found to have been improperly registered to cast ballots.

The Supreme Court announced Thursday it would convene July 10 to hear appeals from Ted Opitz, the Conservative MP whose 2011 election victory was tossed out by an Ontario judge.

Also appealing is the former Liberal MP, Borys Wrzesnewskyj, who lost to Mr. Opitz by 26 votes in what was one of the closest-fought races of the 2011 federal election.

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Mr. Wrzesnewskyj is still arguing there are even more instances of voters casting ballots without properly clearance.

The Supreme Court ends its spring sitting this week and wasn't scheduled to begin its fall sitting until October.

The Tories' Mr. Opitz had told the Court he'd be willing to wait until October to argue the case but the Liberals' Mr. Wrzesnewskyj has pleaded for a quick hearing.

A mid-May poll of Etobicoke Centre voters by Forum Research suggested Mr. Wrzesnewskyj would defeat Mr. Opitz by a 10-point lead if a by-election was held.

This rare case – where a judge has voided the results of a federal election – is apparently considered a sufficient priority to alter the Supreme Court's schedule.

On May 18, an Ontario court judge threw out the results of last year's general election in Etobicoke Centre after he found that officials failed to ensure 79 voters were properly registered or cleared to cast a ballot.

That ruling was only the sixth time since 1949 that a Canadian court has set aside federal election results in a riding.

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The Liberals, preparing for the possibility of a by-election, have already re-nominated Mr. Wrzesnewskyj as their candidate.

"I look forward to attending the hearing on July 10th," Mr. Wrzesnewskyj said.

This fight has so far cost Mr. Wrzesnewskyj about $300,000 of his own money.

The Conservative Party could not immediately be reached for comment Thursday.