An extraordinary showdown between Prime Minister Stephen Harper and Supreme Court Chief Justice Beverley McLachlin has intensified, with the jurist denying wrongdoing, and disputing Mr. Harper's recollection of the facts.

The court issued a statement a little after noon on Friday, defending itself against the top-level attack on its integrity: "At no time was there any communication between Chief Justice McLachlin and the government regarding any case before the courts."

The Prime Minister's Office had levelled a serious, but indirectly phrased, accusation the evening before – that Chief Justice McLachlin tried to involve Mr. Harper in an inappropriate discussion about a case that was either before the court or that could come before the court. If true, the longest-serving chief justice in the court's history might have to resign, or face the unheard-of prospect that the House of Commons and Senate would unite to force her off the bench.

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"The PM is imputing inappropriate interference to the Chief Justice and it's very personal, it's superpersonal," McGill University law professor Robert Leckey said.

Until now, the Conservative government and the country's highest court had wrestled each other in the traditional ways – in court filings and hearings. But after five rulings in as many weeks in which the court rejected key elements of the government's agenda, something changed. Those rulings, in sum, were a rejection of Mr. Harper's long-held views on Parliament's supremacy.

And then, on Thursday evening, Mr. Harper registered a serious allegation against the Chief Justice in the court of public opinion. And the conflict between the court and the government moved on to uncharted ground.

The Chief Justice, the Prime Minister's Office said in a news release, had tried to involve him in an inappropriate conversation about a case.

"Neither the Prime Minister nor the Minister of Justice would ever call a sitting judge on a matter that is or may be before their court," the release said. "The Chief Justice initiated the call to the Minister of Justice. 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."

The case in question was the Supreme Court appointment of Justice Marc Nadon, a member of the Federal Court of Appeal. The Supreme Court Act does not expressly say that Federal Court judges are eligible to fill one of the three spots reserved for Quebec on the Supreme Court. (The court ruled Justice Nadon ineligible in March, the first time in a common-law country an appointed Supreme Court judge had been rejected by a court as ineligible, according to political scientist Carl Baar.)

The PMO's statement follows a recent pattern of blaming the judiciary for the government's inability to move forward on Senate reform, a key concern for many Conservative voters. Last week, Mr. Harper called the court's ruling on the matter a "decision for the status quo," which he said almost no Canadian could support.

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Responding to the PMO's statement, the court said that Chief Justice McLachlin's contact with the Justice Minister occurred on July 31 – two months before Justice Nadon was chosen for the court. The court said she was simply flagging the potential issue around the eligibility of a Federal Court judge. It also said that her office had made preliminary inquiries about contacting the Prime Minister, but that the Chief Justice had decided against it – a much different version from the PMO's statement.

Legal observers, including the Canadian Bar Association, representing 37,000 lawyers and judges, said that they found no fault with the Chief Justice, and that it is common practice in Canada for chief justices to consult with governments during the appointment process. John Major, a former Supreme Court judge, called her contacts with the government "innocuous."

"I don't view it as calling about a case. It's about the operation of the court," he said.

Adam Dodek, a University of Ottawa law professor, said that if the government felt the Chief Justice had acted inappropriately, the Justice Minister had an obligation to publicly challenge her ability to hear the case before it began.

Fred Headon, president of the Canadian Bar Association, said he hopes the PMO's statement was based on a misunderstanding. "It is troubling because it threatens to discredit the chief and the institution of the court and by extension the judiciary throughout Canada."

With a report from Kim Mackrael in Ottawa