Spanish police detained nine people in Madrid in mid-November, including Alexander Gofshtein, a lawyer for the bankrupt Russian oil company Yukos, on a warrant issued by Spain's Audiencia Nacional, or National High Court.
"The Federal Chamber of Lawyers of the Russian Federation, as well as the Moscow Chamber of Lawyers, forwarded a request to the Russian Foreign Ministry to that effect," Yevgeny Semenyako, the head of the Federal Chamber of Lawyers, said.
"We consider the detention and subsequent arrest of lawyer Gofshtein as illegal," he added.
Gofshtein traveled from Moscow to Spain for a meeting in the Soto del Real prison with his client, Zakhar Kalashov, a purported Georgian mafia boss alleged to be involved in money laundering.
Spanish police said earlier in a press release that Gofshtein was arrested as part of a large-scale operation codenamed Operacion Avispa (Operation Hornet), targeting Russian and Georgian mafia members operating in the country.
They said he brought money to his jailed client, Kalashov, whose criminal organization made large sums from criminal operations in Moscow, including illegal gambling, kidnapping and extortion, and then invested it in Spanish real estate, restaurants, and other assets.