Nadon, who was chosen on Sept. 30 to join the Supreme Court, has recused himself from participating in cases while a Federal Court hears the challenge brought by a Toronto lawyer.
Johanne Brodeur, president of the Quebec bar, says Nadon's move means that some important cases will not be heard by a full bench.
For example, when the top court sat earlier this week to hear Mohammed Harkat's challenge of the constitutionality of security certificates, only eight justices were on the bench. Additionally, a case on reform of the Senate is due to begin Nov. 12.
Brodeur said the legal challenge could take years to resolve.
"It has to go to Federal Court, and Court of Appeal. It could take up to five years or more," she told CBC's James Fitz-Morris.
Even if the case is fast-tracked directly to the Supreme Court, she said, it could possibly take up to two years.
At issue are the rules of who may be appointed to the country's top court. Nadon would seem to meet the general qualifications, but doesn't seem to fit the special requirements outlined for the three judges representing Quebec, guaranteed under the law.
The dispute is over whether Nadon is an advocate of the province of Quebec, given he spent the last nine years as a Federal Court judge in Ontario.
Rocco Galati is the constitutional law expert and lawyer who brought forward the case. His argument is that only judges from Quebec's appeals or superior courts, or lawyers who have been members of Quebec's bar for at least 10 years, can be appointed to the Supreme Court.
"I have severe doubts on the propriety — the statutory and constitutional propriety — of this appointment," he said.
University of Ottawa faculty of law professor CarissimaMathen said the law is unclear, at best.
"We're really in virgin territory here," she said. "This is really unprecedented."
Regardless of whether the matter works its way through the court system or is expedited straight to the top court, Mathen said the Supreme Court will have to rule on itself.
"I think the optics are very unfortunate, and it puts the court, it puts all the justices in a very difficult position."
The federal government evidently knew that selecting Nadon could cause problems. Prior to selecting Nadon, the government sought a legal opinion from Ian Binnie, a retired Supreme Court justice, who backed the appointment.
Federal Justice Minister Peter MacKay said he will defend the rights of Quebecers from the Federal Court to sit in the Supreme Court, but so far hasn't moved to expedite the challenge against Nadon or explain why he hasn't.
The Supreme Court won't say what Nadon is currently doing because the matter is before the Federal Court.