Counsel Peter Ramesh Kumar told IANS that the mercy plea was filed on Wednesday, under Article 72 1B of the Constitution.
Earlier, Ramesh Kumar had said that since Karnan is set to retire in June, sentencing him to jail will delay clearance of his retirement benefits.
High Court judges get paid out of the Consolidated Fund of India.
Justice Karnan was found in contempt of court for hurling corruption charges against Supreme Court and High Court judges.
On May 11, the Supreme court was moved seeking suspension of the six-month sentence.
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