The heady days of medical marijuana dispensaries piling their back rooms with grocery bags full of cash could soon be a thing of the past, as a new bill making its way through Congress could make it easier for these businesses to obtain bank accounts.

In a bipartisan vote, the US House of Representatives passed an amendment this week that would effectively block the US Department of the Treasury from penalizing banks choosing to work with state-legal marijuana businesses. The amendment was proposed by representatives from Washington, Colorado, and California — three states that benefit from tax money funneling through their legalized recreational or medical marijuana industries.

The bill still needs Senate approval, but the House vote in itself sends a strong message to banks that may want to work with state-legal marijuana businesses but fear repercussions from the Treasury. Banks doing business with these entities can currently be charged with helping to facilitate money laundering — even in states where the operations are legal.

Nearly half of US states have legalized marijuana for medicinal purposes, including the District of Columbia. Colorado and Washington began controlling recreational marijuana use along the same lines as alcohol this year, and Oregon and Alaska will vote to do the same in November.

Despite legalization trends, on-the-books marijuana businesses have had a hard time functioning smoothly without crucial operational elements like bank accounts. Business owners have been forced to keep the cash on hand.

In January, Denver dispensary owner Kristi Kelly told the New York Times that she’d had to open six bank accounts in 18 months. The accounts kept getting closed; obtaining the account in the first place was no problem, but the high levels of cash kept flagging the bank’s compliance rules.

This kind of massive cash stockpiling situation can create security risks. Former chief prosecutor and Seattle resident Jim Doherty told VICE News if banks won’t work with Washington state’s legal marijuana businesses, the buck is ultimately passed to law enforcement.

“It’s a danger to the public," he said. "The sheriff of King County testified about this months ago; they’re very concerned about robberies because people know there’s large amounts of cash."

And it’s not just banks that have been shy about working with the retail pot businesses in Washington and Colorado — or the medical marijuana dispensaries in 23 US states and DC. It has been so hard for people in the industry to get and keep credit cards that companies like MJ Freeway, Proteus 420, and Café Cartel have launched point-of-sale systems designed specifically for medical and state-legal marijuana businesses.

'The conflict between state and federal law is only growing.'

National affairs director for Drug Policy Alliance Bill Piper told VICE News that in many cases the banks’ concerns are overblown.

“There’s the issue of what the Treasury Department will do, but then there’s the fear that the banks have of what they will do,” Piper said. “The fear is probably greater than the actual bite. The value of this amendment is that it shows the politics have shifted.”

For the Drug Policy Alliance, the vote is also a sign that federal decriminalization is on its way.

“The conflict between state and federal law is only growing,” Piper added. “If you get the states to opt out, the federal government doesn’t have the resources to do it alone, and it has to change policy.”

For decriminalization advocates, this is the fourth major win in the House this year. Representatives have already passed an amendment barring the DEA and Department of Justice from using funding to undermine medical marijuana legislation, and two amendments blocking federal interference with state hemp laws.

Increasingly, the Congressional message is clear: The federal government needs to get out of the way of state laws when it comes to marijuana.

“The war on marijuana is definitely going to end," Piper said. "It’s just a question of when at this point."

Follow Mary Emily O’Hara on Twitter: @maryemilyohara