In his 25-page decision, Superior Court Justice David Stinson refused to grant an injunction against the provision that strips the use of voter information cards as a form of identification.
"It is problematic to change the rules for elections at the last minute through the blunt instrument of judicial intervention," Stinson wrote.
"Late changes in election rules run the risk of unfairness or, at the very least, the perception of unfairness."
The Council of Canadians, Canadian Federation of Students, and three voters argue parts of the Fair Elections Act enacted last year are unconstitutional. They maintain that thousands of people could be disenfranchised by the new law — mostly students, aboriginals, seniors and the homeless.
However, because the case can't be resolved before the election — which must take place Oct. 19 at the latest — the applicants asked Stinson to grant an injunction against the provision that ends the use of the voter information card as ID.
Even though the applicants have raised a serious case and some voters might suffer "irreparable harm" by not being able to exercise their right to vote, Stinson said, he couldn't grant the requested relief.
The provision at play, the justice pointed out in his decision, was only one of several in the new law.
"To pick and choose among them without considering the overall scheme runs the risk of unfairly isolating or highlighting concerns arising out of one specific provision without considering the impact and context provided by the rest," he said.
"It is inappropriate to venture a guess as to the constitutionality of the provisions not before me, or to determine the constitutionality of an entire scheme in light of one provision."
As part of the new rules, the government stripped Canada's chief electoral officer of the right to recognize the information cards as a valid form of identification. The government maintains the new rules are needed to prevent voter fraud.
The federal Liberals said they would repeal the law if elected and restore the information card as a form of ID.
"Conservatives have changed our election laws to make it harder for Canadians to vote, easier for parties to cheat, and more difficult to catch rule breakers," Liberal critic Scott Simms said in a statement.
Garry Neil, executive director of the Council of Canadians, expressed disappointment at the ruling, but said the fight would continue beyond the next election.
"We're not deterred," Neil said. "We are going to see the case through to the end."
Bilan Arte, national chairman of the Canadian Federation of Students, said in a statement the organization would ensure students have access to information on how they can vote "in spite of this government's voter suppression laws."
In the 2011 election, as many as 400,000 people used voter information cards as official ID on election day. The cards are one of the few forms of readily available ID with an elector's address but the government notes 45 acceptable forms of ID are available.
Note to readers: This is a corrected story: The election must be held on or before Oct. 19. An earlier version said Oct. 17.
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