A judge who wore a pro-Trump hat into his courtroom should be publicly condemned and disciplined, an Osgoode Hall law professor says in a formal complaint to a judges' disciplinary body.

On Wednesday morning, after the U.S. presidential election, Judge Bernd Zabel of the Ontario Court of Justice in Hamilton wore Mr. Trump's "Make America Great Again" campaign ball cap when he entered his courtroom, a source who was in court told The Globe and Mail. He said the cap signified that it was an historic occasion. He removed the cap and put it on the bench in front of him, the source said, and returned with it after the court's morning break.

Citing The Globe's report, law professor Gus Van Harten complained in writing to the Ontario Judicial Council on Friday. He said Judge Zabel's "childish" conduct cast doubt not only on the fairness of his courtroom but that of the entire Ontario Court of Justice, whose judges sit throughout the province. And he said the judge should at the very least be made to withdraw from cases involving minority groups disparaged by president-elect Trump during the campaign.

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These steps, Prof. Harten said in his complaint, are needed to "reassure members of relevant groups who will in future be subject to Justice Zabel's now-tainted authority and the authority of Ontario courts."

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If the council investigates and decides his complaint is warranted, it could lead to a public hearing and ultimately result in penalties, from a warning to a recommendation that the judge be removed from office.

The case of Ontario Superior Court Justice Antonio Skarica – who wore a Trump "Make America Great Again" T-shirt while out shopping one day last spring – provides an indication of how seriously judicial authorities take such complaints.

Lorne Warwick, a retired teacher from Dundas, Ont., complained to the Canadian Judicial Council, the disciplinary body for federally appointed judges. The CJC referred the complaint to the chair of its conduct committee, Nova Scotia Chief Justice Michael MacDonald. He spoke to Justice Skarica, who told him he had not intended to make a political statement; he had received the T-shirt from his brother and considered it an item of memorabilia. He promised not to wear the shirt in public again, according to a letter from the CJC that Mr. Warwick posted on a blog.

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A spokeswoman for the CJC confirmed the authenticity of that letter. "I believe it shows we took the matter seriously, seeking comments from the judge, and carefully considering the matter following Chief Justice MacDonald's direction," Johanna Laporte said in an e-mail.

Mr. Warwick said in an interview that he was "astounded" when he and his wife saw Justice Skarica in the Trump T-shirt. "I felt his judgment was very bad." He said other shoppers who recognized Justice Skarica looked at him "with disgust." But at least the judge had to account for his "strange behaviour," he said in his blog post.

Judge Zabel, who specialized in criminal law and family law before becoming a judge, was appointed to the bench in 1990 by Liberal attorney-general Ian Scott. That came in the first batch of appointments under the province's new system, meant to reduce the role of politics in appointments by establishing a committee of lawyers, judges and laypeople that would make recommendations to the attorney-general.

A graduate of the University of Windsor law school, he was called to the bar in 1979. He is a past president of the Hamilton Criminal Lawyers Association, and a former director of the Elizabeth Fry Society of Hamilton.

Judge Zabel did not return phone calls to his office Thursday and Friday.