Attorneys general in 19 states and U.S. territories say Congress must act to end the banking industry’s prohibition on serving the marijuana industry, calling the current state of affairs a public safety threat and a hindrance for law enforcement.

In a letter to leaders of the House and Senate, the attorneys general urged Congress to pass legislation that would provide legal protection for banks that accept deposits from state-licensed cannabis businesses.

Most banks, even in states where the drug is legal, won’t offer accounts to marijuana-related businesses for fear of running afoul of federal officials. That leaves the fast-growing marijuana industry largely reliant on cash.

This “gray market,” state officials argue, makes it more difficult for states to ensure that businesses are paying their taxes, and “contributes to a public safety threat as cash-intensive businesses are often targets for criminal activity.”

Giving banks the go-ahead to work with cannabis companies “would bring billions of dollars into the banking sector, and give law enforcement the ability to monitor these transactions,” the letter says.

The letter came about a week after U.S. Attorney General Jeff Sessions revoked some of the agency’s Obama administration guidance regarding cannabis law enforcement, an action that some suggest could lead to a federal crackdown.

“The recent rescission of that guidance has made the need for congressional action to get the cash generated by this industry into a regulated banking sector even more urgent,” they wrote.