By Lisa Lambert

WASHINGTON (Reuters) - The U.S. government should keep banks from cutting off the accounts of vendors who work with state-sanctioned marijuana businesses, 10 U.S. senators said in a letter to the Treasury on Wednesday.

Medical or recreational use of marijuana is legal in more than half the 50 U.S. states and the District of Columbia, and the list is growing with voters in eight states approving pot-related ballot measures last month.

The drug is still deemed illegal by the federal government. Guidance it issued in 2014 on how to provide financial services to state-approved marijuana dispensaries without running afoul of U.S. law, has spooked banks and credit unions from taking accounts in the cannabis industry.

That nervousness has spread to landlords, security guards, chemists, lawyers and other vendors working with marijuana businesses, according to the lawmakers, who included Republican Lisa Murkowski of Alaska, where commercial marijuana has been legal since 2014.

Eight Democrats, including Massachusetts' Elizabeth Warren and Oregon's Jeff Merkley, and Bernie Sanders, the Vermont independent who ran for the 2016 Democratic presidential nomination, also signed the letter.

"Most banks and credit unions have either closed accounts or simply refused to offer services to indirect and ancillary businesses that service the marijuana industry. A large number of professionals have been unable to access the financial system because they are doing business with marijuana growers and dispensaries," they wrote.

The Treasury Department's Financial Crimes Enforcement Network is reviewing the letter, according to a spokesman.

Members of both parties have embraced making banking easier for marijuana-related businesses. Some Republicans believe states have the right to choose how to treat marijuana, and many, including President-elect Donald Trump, believe the drug could have medical benefits.

Adamantly opposing loosening restrictions on pot is Senator Jeff Sessions, Trump's pick for attorney general.

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The marijuana industry sees challenges in Sessions becoming the country's law enforcement officer but does not anticipate immediate federal threats if he is approved, said Robert Capecchi, a lobbyist with the Marijuana Policy Project.

The federal government cannot conscript local law enforcement and would have to send its own forces to crack down on marijuana businesses, at a significant cost, he said.

"I don't think they're going to aggressively go after the businesses and I really don't think they're going to start arresting patients," he said. "I cannot imagine individuals in Mississippi want their tax dollars to go toward breaking up medical marijuana businesses in Connecticut."









(Reporting by Lisa Lambert; Editing by Peter Cooney)