Canada's high court on Friday rejected Prime Minister Stephen Harper's appointment of a like-minded justice to the top court, saying the vacancy must be filled by a judge or lawyer from Quebec.
In a 6-1 decision, Supreme Court justices barred Marc Nadon from taking a vacant seat alongside them, noting that it is one of three reserved for Quebec judges or lawyers.
The ruling is historic and a blow for the Harper government, which has sought to reshape the bench to reflect its socially conservative values.
It comes at a time when the high court is wrestling with the constitutionality of anti-terror measures, proposed Senate reforms and other major legal issues facing Canada.
Nadon's appointment had faced fierce opposition from the government of Quebec and from a Toronto lawyer who challenged the appointment on the technicality mere hours after it was announced last October.
Nadon stepped aside the following day to allow the high court to rule on the matter.
Nadon, 64, practiced law for 20 years in the Canadian province of Quebec, which is unique in Canada for adhering to a French-heritage codified civil law, instead of common law. But for the past two decades he has sat on the federal court.
"The role of Quebec judges on the federal courts is a vital one," the majority of justices said in the decision.
"The question is not whether civilist members of the federal courts would make excellent judges of the Supreme Court of Canada, but whether they are eligible for appointment (under the rules) on the basis of being former rather than current advocates of the province of Quebec.
"We conclude that they are not."
The lone dissenter, Justice Michael Moldaver, said judicial appointments are strictly matters for the executive branch of government to decide, and not the court.
The decision however arguably leaves room for Nadon to resign from the bench, then rejoin the Quebec bar for a day to qualify.