U.S. banks in Colorado and Washington state, where voters last week legalized recreational marijuana use, shouldn't disregard federal laws that consider pot sales criminal, a bank regulator said today.

"I think institutions have to protect themselves," said Daniel Stipano, acting chief counsel of the Office of the Comptroller of the Currency, at an anti-money laundering conference today run by the American Bankers Association. "The problem is that it remains a crime under federal law." The Bank Secrecy Act requires banks to file suspicious-activity reports if they suspect customer's involvement in federal crimes. It's meant as a protection against U.S. financial institutions being used to launder illegal gains from criminal activity.

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"If there was ever an area crying out for guidance, this is it," said Stipano, whose agency regulates national banks. "As a government we need to be clear on this and speak with one voice," he said, adding that this new legal clash puts financial institutions in "a tough spot" when regulated marijuana retailers seek banks to aid in their money management.

"My opinion would be, if you want to open the account, go ahead," said Richard A. Small, a former Federal Reserve deputy associate director who now handles anti-money laundering compliance at American Express Co. "But every time you take in money, you file a suspicious-activity report, because you do have a violation of the law."

Teresa A. Pesce, who heads the anti-money laundering group at KPMG LLP, said banks should continue to see the business as a federal crime and offered this advice: "Don't do anything different."

Washington state will allow those at least 21 years old to buy as much as one ounce (28 grams) of marijuana from a licensed retailer. Colorado's measure allows possession of an ounce, and permits growing as many as six plants in private, secure areas. Oregon voters rejected a similar measure.