TORONTO -- Canada's top court is set to grapple with whether long-term expats should be allowed to vote, an issue that loomed large in the last federal election in which Justin Trudeau and his Liberals took office.

Civil liberties groups, which argue current rules barring the expats from voting are unconstitutional, and Quebec, which supports the federal government's defence of the restrictions, are among interveners in the closely watched case the Supreme Court of Canada is scheduled to hear on Wednesday.

Canadians lose the right to vote after living abroad for more than five years under rules on the books since 1993. However, it was only under the former Conservative government of Stephen Harper that Elections Canada began enforcing the laws.

Two Canadians living and working in the United States launched the case after being denied the right to vote in the 2011 election. They argue that citizenship, not residency, is the key requisite for voting.

"One way or the other, this is going to get decided and either Canadians will be enfranchised or Canadians will be disenfranchised," Jamie Duong, one of the appellants, said from Ithaca, N.Y.

Duong and Gill Frank, an academic in Princeton, N.J., initially won their case before Ontario Superior Court in 2014 but the government appealed. In a split decision in 2015, the Ontario Court of Appeal ruled the restrictions do indeed infringe on the rights of citizens. However, the majority found the violation democratically justified because the rules preserve the "social contract" between voters and lawmakers.

In its Supreme Court filing, the government takes issue with the characterization that long-term expats were "disenfranchised" by the rules enforced under Harper. With few exceptions, no Canadians living abroad were allowed to vote before the 1993 law changes, the government says.

"The impugned provisions enfranchised non-resident citizens by allowing them to vote for the first time in Canadian history, for as long as they met the definition of being temporarily resident outside Canada," the government states.

In their factum, Duong and Frank argue they maintain a "deep and abiding" connection to Canada even though, like many citizens in a globalized world, they have left the country for employment or educational reasons.

"There is no pressing and substantial objective to justify the legislation," the pair argue. "Five years is an arbitrary marker, which is not rationally linked to a citizen's connection to Canada, nor to being subject to Canadian laws."

Another intervener, the Canadian Expat Association, said the rules have "devalued" the citizenship of those abroad.

"For expats whose identity is deeply Canadian, this expressive harm to their dignity and personhood is demeaning and harmful," the association says.

In rebuttal, the federal government argues Parliament made a reasonable policy choice in enacting rules designed to maintain the fairness of the electoral system. Canadians living in Canada, the government maintains, are more affected by laws their elected officials enact than are expats.

During the last election, actor Donald Sutherland, Canadian business groups abroad and other expats rallied against Harper and the voting ban. The campaigning Liberals promised a review and in November 2016, the Trudeau government introduced legislation to enable Canadians abroad to vote. However, little has happened since.

Duong said expats -- estimates are that more than one million of them are unable to vote -- will be keeping a close eye to see what the Supreme Court decides.

"The Canadian expat community that has been supporting us and supporting the fight has been fantastic," Duong said. "We've raised closed to $18,000 from 220 people around the world...that has been helping to cover court expenses."