Oregon Attorney General Ellen Rosenblum and her peers from 19 other states wrote to Congressional leaders today seeking an expansion of banking options for businesses engaged in the legal cannabis trade.

The letter comes less two weeks after U.S. Attorney General Jeff Sessions suspended the Cole memo, an Obama-era document that said federal law enforcement officials would not prosecute the marijuana industry in states where the drug is legal.

The state AG's want Congress to address a large and growing problem.

Because federal law does not recognize the legality of marijuana, banks are reluctant and in most cases unwilling to accept deposits or provide other financial services to cannabis businesses, even in states where weed is legal.

"We urge Congress to advance legislation that would allow states that have legalized medical or recreational marijuana to bring that commerce into the banking system," the letter says.

Medical marijuana is now legal in 29 states. Eight of those states and the District of Columbia have also legalized recreational marijuana.

The AGs' letter says the size of the legal cannabis industry was $6.7 billion in 2016 and will grow to $20 billion by 2021. That's a lot of cash that is currently flushing around the system. Without the opportunity to deposit it in banks, businesses are subject to security risks and the temptation to invest in illegal activities.

"The recent rescission of [the Cole memo] has made the need for Congressional action to get the cash generated by this industry into a regulated banking sector even more urgent," the letter says.