As a result, the International Commission of Jurists says Harper should withdraw his remarks and he and Justice Minister Peter MacKay should apologize to Beverley McLachlin, chief justice of the Supreme Court of Canada.
The opinion by the Geneva-based organization follows a complaint from a group of Canadian lawyers and legal academics related to the federal government's abortive appointment of Federal Court Judge Marc Nadon to the top court in October last year.
Harper and MacKay would later suggest publicly that McLachlin had behaved inappropriately by trying to talk to them about potential legal problems with the proposed appointment.
Their comments were out of line, the jurists said in a written opinion released this week.
"The (commission) sees no necessity for them to have aired their opinions on this matter several months after the fact, in public, and in a manner that impugned the propriety of the chief justice's actions," the opinion states.
"The criticism was not well founded and amounted to an encroachment upon the independence of the judiciary and integrity of the chief justice."
If Harper or MacKay had any issues with how McLachlin had behaved, the review states, they should have handled the matter confidentially, not made public comments.
Harper's communications director Jason MacDonald had little to say in response.
"We have seen the letter," MacDonald said in an email Friday. "We have noted it. I have nothing further to add."
MacKay's office had no comment.
The commission — which did not receive requested input from Harper's office — also urged the government to rethink the opaque process by which it now appoints judges.
What's needed is an "open process with prescribed criteria based on merit and integrity and without discrimination," the commission says.
Harper's appointment of Nadon — despite McLachlin's effort to "flag a potential issue regarding ...eligibility" — led to a successful constitutional challenge that ultimately scuttled his ability to take his place on the court.
The appointment and Harper's subsequent comments in May that he had ignored her advice because it would it would have been improper to listen to her sparked a furor among many in the legal community, who rushed to her defence.
In a statement in May, MacDonald said McLachlin had called MacKay to discuss the Nadon appointment.
"After the minister received her call, he advised the prime minister that, given the subject she wished to raise, taking a phone call from the chief justice would be inadvisable and inappropriate,'' MacDonald said. "The prime minister agreed and did not take her call."
A day later, Harper himself said it would have been wrong to talk to McLachlin given that the Nadon appointment was subject to a legal challenge.
The comments prompted the chief justice to issue a rare statement saying she had not tried to weigh in on Nadon's appointment, only to point out potential problems.
The commission comprises 60 eminent judges and lawyers from around the world and works to promote and protect human rights through the rule of law.
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