The final stages of a $22.5 billion battle pitting the Bank of New York Mellon against the Russian Federation will begin today in a Russian court.

The decision in the money laundering suit, which may be handed down as early as this week, could set a precedent for the global application of the Racketeer Influenced and Corrupt Organizations Act, on which the suit is based. The case is troubling some lawyers, who say the Russians are applying the RICO statute piecemeal, and should they win it would be with an unorthodox version of the law that lacks some of the checks and balances used in the American court system. It could also pose risks for American companies other than the Bank of New York Mellon that are operating in Russia or its allied countries.

“This is a legal nightmare,” a professor of law at Columbia Law School, John Coffee, said. “Everyone who hears about it is frightened because the Russians are writing the rules as they go.”

The Russian Federal Customs Service is suing the bank in the Moscow Arbitration Court over a money laundering scheme from the 1990s, when two Russian émigrés moved $7.5 billion to American accounts from Russia via unlicensed wire transfers. The Bank of New York, which was founded by Alexander Hamilton in 1784, paid a fine for failing to monitor the accounts, and a former bank executive, Lucy Edwards, a Russian national, and her husband, Peter Berlin, pleaded guilty to money laundering.

The Russians claim that they, too, should receive compensation, and they are asking for $22.5 billion based on the RICO treble damages rule. Experts say it is very rare or even a first for the racketeering statute to be argued in a foreign court.

The court will hear testimony today from a number of experts, including a former U.S. attorney general and governor of Pennsylvania, Richard Thornburgh, and a former chief judge on the U.S. Court of Appeals for the District of Columbia Circuit, Abner Mikva. The two will join 17 Russians in testifying on behalf of the Bank of New York Mellon. The plaintiff, meanwhile, will present testimony from G. Robert Blakey, who is credited with drafting the original RICO statute, and a Harvard Law professor, Alan Dershowitz, who has been retained by the plaintiff, may also present testimony.

Among the possibilities should Russia win is that the Bank of New York Mellon could see all of its assets in Russia seized. While in America the RICO act allows the so-called forfeiture sanctions only if the company is being pursued by a U.S. attorney general, it is possible that the Russians could disregard this rule and decide the bank must forfeit its assets as a way to pay the damages. Another potential liability is that Russia could seize any payments that a Russian third party is making to the bank.

“This is Mother Russia we are talking about here, so anything is possible,” a professor of law at Johns Hopkins University, Ruth Wedgwood, a former federal prosecutor, said. “Their court judgment is suspect.”

For Mr. Dershowitz, the use of the RICO statute in Russia has greater significance than whether the Russians are following all of the rules. “I am delighted about the precedent this lawsuit will set,” he said. “I have people lining up to take my services, and I pick and choose. I decided to take this case because I am interested in a broad application of money laundering as it relates to fighting global terrorism.”

The Bank of New York Mellon operates in more than 90 countries, and it is not likely that American or Western European courts would uphold a Russian court’s judgment against it, experts said. If the bank loses the case, it would likely have to discontinue its Russian operations at the very least. “The existence of a huge unsatisfied judgment against the bank would effectively preclude it from doing business in Russia,” Mr. Coffee said.

Despite statements by the new Russian president, Dmitry Medevedev, that he wants to clean up the court system, should the Bank of New York Mellon lose the case, it could exacerbate tensions between the Kremlin and non-Russian companies. This is especially true in light of the ongoing disputes between the government and the oil company BP.

“This is not a good time for an American bank to tussle with Russian authorities,” a resident scholar and director of Russian studies at the American Enterprise Institute, Leon Aron, said. “Russian domestic legitimacy comes from confrontation with the West, and while they are interested in making money like capitalists, Russians are really more mercantilists — they want to make money, yes, but use their economic achievements to promote the state’s goals.”