Moscow Mayor Yury Luzhkov has announced that he and his wife, Yelena Baturina, have filed a lawsuit against opposition activist Boris Nemtsov, RFE/RL's Russian Service reported.
Luzhkov said that Nemtsov's recent brochure, "Luzhkov, Itogi" (Luzhkov, the Results), is untrue and therefore libelous.
Nemtsov -- cochairman of the opposition Solidarnost (Solidarity) movement -- writes about Luzhkov's activities as mayor in the brochure.
He alleges possible improprieties between Moscow city officials and the Inteko company, which is owned and run by Baturina.
Nemtsov is a former deputy prime minister and a cofounder of the Union of Rightist Forces.
He has long been an outspoken critic of Prime Minister Vladimir Putin.
Nemtsov told RFE/RL that he is ready for any court hearings against him, adding that he has the necessary documents to back up the claims he makes in his brochure.
Luzkhov has been mayor of Moscow since 1992.
His wife is thought to be the richest woman in Russia, with an estimated net worth of more than $1 billion.