Canada's highest court will issue its ruling Thursday morning on whether Opitz legitimately won his seat in the Toronto riding of Etobicoke Centre in the May 2011 federal election.
Opitz is appealing an Ontario Superior Court ruling that set aside his narrow, 26-vote victory in Etobicoke Centre over Liberal incumbent Borys Wrzesnewskyj, after identifying procedural irregularities with 79 ballots.
It will be first time the Supreme Court has ruled on the validity of an election result in a federal riding.
Opitz's office says he won't be joining 10 fellow MPs from the Conservatives, NDP and Liberals who were to depart Ottawa on Wednesday to monitor Sunday's parliamentary elections in Ukraine.
His office says Opitz still hopes to go on the mission, depending on the ruling.
Seven justices of the high court heard Opitz's appeal at an emergency hearing in July and have been working on the decision since.
There is no evidence that either of the candidates — or either of the two federal parties — engaged in fraud or corruption.
Ontario Superior Court Justice Thomas Lederer threw out Opitz's victory because he found irregularities with 79 ballots. The problems related to how new voters were registered on Election Day, and whether the accompanying paperwork by Elections Canada staff was adequately done.
Wrzesnewskyj cross appealed and asked that more ballots be rejected.
He also argued that some voters may have been allowed to cast ballots twice.
Wrzesnewskyj said Wednesday he planned to be at the Supreme Court for the decision. It will be made public in written form at 9:45 a.m. ET, as per the court's custom.
Conservative party spokesman Fred DeLorey wouldn't say whether Opitz will be at the court as well.
The ruling could have wide-ranging implications for all future elections in Canada.
The ruling will be precedent setting because it is expected to set out clear rules on when the courts ought to involve themselves in reviewing tight election races — and when they should not.
The court will have to decide whether polling officials made errors, and it whether those errors actually had any impact on the final result.
Elections Canada says that no election is perfect, but they have challenged Wrzesnewskyj's argument that systemic problems caused his defeat.
Opitz's lawyers argued that if Lederer's decision is allowed to stand it will "undermine, rather than enhance, the respect and confidence that ordinary Canadians have for the electoral process in this country."