Robert Schulz, who has successfully sued past state officials, says Silver's settlement of accusations against Assemblyman Vito Lopez violated the state constitution.
Schulz tells The Associated Press that Silver couldn't use public funds to pay for a "private undertaking."
Silver has apologized for the 2012 settlement and is pushing reforms to make sure established procedure is followed for any future sexual harassment allegations.
Lopez has denied any harassment. He resigned from the Assembly in May and is running for New York City Council.
Silver's spokesman had no immediate comment. Schulz filed the suit Thursday.
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