The Conservative government is headed toward another legal battle – perhaps more than one – in its apparent pursuit of another judge for the Supreme Court of Canada.

Fresh from an unprecedented and unsuccessful six-month fight over its choice of a judge for the top court, the government appears to have chosen another judge from the source recently ruled ineligible – the Federal Court in Ottawa. This time, it has taken an intermediate step: It is moving a probable candidate from that court to the Quebec Court of Appeal effective July 1. This would make him eligible to be appointed to the Supreme Court when a Quebec seat opens in December with the retirement of Justice Louis LeBel.

On Monday morning, Rocco Galati, the Toronto lawyer who brought the appointment of Justice Marc Nadon to a screeching halt last October, filed a challenge to the appointment of Justice Robert Mainville to the Quebec Court of Appeal, and asked for a declaration that a subsequent Supreme Court appointment would be illegal.

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Justice Minister Peter MacKay appeared to confirm that the government is indeed planning to appoint Justice Mainville, currently of the Federal Court's appeal division, to the Supreme Court, describing him as a judge who is worthy of the highest court in the land. "I believe his wealth of legal knowledge will be welcome at the Supreme Court and will be of significant benefit to the Quebec Court of Appeal," he told the Commons. Later, he said he did not not mean to refer to the country's top court.

The appointment of Justice Mainville, which a source said was worked out about a month ago, would help Ottawa avoid having to ask the Quebec government for a list of candidates, as it did this spring to replace Justice Nadon.

Justice Mainville, an expert in aboriginal law, was on the government's confidential list of six candidates for the previous vacancy, which was obtained by The Globe and Mail. Justice Mainville was also on the list of candidates for the 2012 vacancy, which was filled by Justice Richard Wagner, a source told The Globe.

In the new court challenge, Mr. Galati cited the fact that Justice Mainville was on the government's list of candidates the last time, saying in a court document that it highlights Mr. MacKay's "abuse of his office in circumventing the clear terms of the Constitution, and ruling of the Supreme Court of Canada, in his unconstitutionally obstinate insistence" on naming Federal Court judges to the Quebec courts and to the Supreme Court.

He pointed to Section 98 of the 1867 Constitution Act, which sets out that judges of the Quebec courts must be chosen from members of the Quebec bar, and said that in the Nadon case, the Supreme Court made it clear Federal Court judges are not members of the Quebec bar.

"This is just unbelievable, mind-staggering," he said in an interview. "This government either chooses to or likes urinating on the Constitution. They simply can't accept the ruling of the Supreme Court and they can't accept the clear terms of our supreme law." Three spots are reserved for Quebec judges on the Supreme Court to ensure current knowledge of the province's civil code. Justice Mainville practised law for three decades in Montreal before he was appointed to the Federal Court in 2009.

Justice Nadon had just been sworn in to the Supreme Court in early October when Mr. Galati filed his challenge. Justice Nadon stepped aside pending the outcome of the challenge. The government later asked the Supreme Court for an advisory opinion on the legality of the appointment. It ruled 6-1 in March that Federal Court judges are not eligible because they lack current Quebec qualifications as set out under the Supreme Court Act. The court was short one judge for 10 months, until last week, when Justice Clément Gascon of the Quebec Court of Appeal was sworn in.

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Whether Justice Mainville will be sworn in to the Quebec Court of Appeal is not clear, and he did not respond immediately to a request through the Federal Court of Appeal for comment.

Legal experts interviewed in Quebec were not sure whether the appointment is legal. Some felt it is, saying that most judges on the Quebec Court of Appeal were appointed from the Quebec Superior Court, where they were not deemed members of the Quebec bar either. (Mr. Galati rejects this point, saying the move is a promotion, not a new appointment.) Justice Joseph Robertson of the New Brunswick Court of Appeal was appointed by a Liberal government from the Federal Court of Appeal in 2000. The wording that covered his appointment, found in Section 97 of the Constitution Act, is largely the same as that covering the appointment of Quebec judges in Section 98.

Even if the appointment is ruled legal, the Supreme Court would be asked to decide if a subsequent appointment to the top court met the spirit and letter of its ruling in the Nadon case.