State and federal authorities have allowed marijuana businesses to keep firearms in-house in Colorado because of the danger posed by operating a cash-only business, a legal expert said Monday.

Jack Finlaw, chief legal counsel to Gov. John Hickenlooper, said Colorado is alone in its tolerance of firearms at marijuana facilities — a practice that runs contrary to recently issued federal guidelines.

A federal rule barring banks from taking the money of criminal enterprises, which marijuana stores are considered under federal law, has scared banks away from doing business with the new industry in Colorado and Washington. Without that relationship, marijuana businesses are forced to accept cash only.

“It’s really an all-cash business, and there’s really a public safety issue with businesses that are dealing with so much cash,” Finlaw said at the Inter American Press Association’s 69th General Assembly.

Finlaw said John Walsh, U.S. attorney for Colorado, has been more lenient than his counterparts in Washington, the only other state where recreational marijuana is legal.

Federal authorities in Washington state have strictly forbidden firearms from marijuana farms and stores, but Finlaw said Walsh “at least understands” their use while the banking restrictions remain.

Finlaw spoke less than three weeks after Hickenlooper and Washington Gov. Jay Inslee urged federal financial officials to exempt marijuana facilities from the banking rule.

In late August, the Department of Justice wrote a letter to federal prosecutors that included the department’s eight expectations for enforcement in states with legalized marijuana. One is to prevent the use of firearms in the cultivation and distribution of marijuana.

On Sept. 10, Deputy U.S. Attorney General James Cole told a Senate committee that the justice and treasury departments were brainstorming how to work around pot shops’ banking problem, but no action has resulted.

Alison Noon: 303-954-1223, noon@denverpost.com