Halyvourgiki Inc., a Greek steelmaker that says it competes with a client of Citigroup Inc., is suing a Citi unit that it claims published a "malicious" research note on the Athens company.

The research note from Citigroup Global Markets contained "falsehoods" about Halyvourgiki's revenue, market share, and investments, the company said in the lawsuit, which was filed in London in September and released by the court Wednesday. The data was published in 2007 alongside accurate figures about Sidenor SA, a publicly traded Citigroup client that competes with the closely held Halyvourgiki, the lawsuit said.

Citigroup "stands to benefit or profit commercially, and/or in terms of its enhanced business reputation from disparaging or inhibiting investment in rival companies of Sidenor's," Halyvourgiki said in the lawsuit, which seeks undisclosed damages and an injunction to stop further publication.

British regulators said in March of last year that they were investigating allegations that traders are spreading false rumors to manipulate share prices. It is the first time a bank has been sued in the U.K. over a research note, lawyers said.

Citigroup said it considers the lawsuit without merit and that it will defend its position vigorously.

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