WASHINGTON — At the Cannabis Club Collective in Tacoma, Brian Caldwell has installed a top-of-the-line alarm system, motion sensors and a safe, hoping to protect the cash he collects from the 200-plus customers who buy marijuana at his store on an average day.

“We pretty much had to make a bank within our walls,” he said.

And at Auntie Dolores, a marijuana edibles shop in Oakland, Calif., Julianna Carella uses pouches to bag her cash at the end of the day, then sticks it in her trunk, feeling nervous as she drives away.

“It’s actually a huge headache to have to deal with all that cash. … It’s horrible,” she said.

While voters in Washington and a growing number of states have embraced marijuana in recent years, federal law still prevents pot businesses from using checks and credit cards offered by banks. That means that by law, they can deal only in cash.

Reviving a fight that stalled last year, the all-cash establishments and their allies in Congress are pushing hard again to change the law, convinced that marijuana shops have become inviting targets for thieves.

“Quite literally, you have accountants stuff $50,000 worth of cash in their backpack and walk it to a depository,” said Rep. Denny Heck, D-Wash., a member of the House Financial Services Committee. “This is a recipe for mischief if we don’t solve it.”

There’s a new twist in this year’s debate, with some in the cannabis industry suggesting that foreign banks or American Indian-owned financial institutions could serve as alternative depositories if Congress doesn’t provide a fix.

Many say the situation is bound to worsen as marijuana grows in popularity and markets expand.

So far, voters in Washington, Colorado, Oregon and Alaska have approved the use of marijuana for recreational purposes, while 23 states allow it for medical reasons. And California voters, who in 1996 made the Golden State the first to back medical marijuana, are expected to decide a ballot initiative on recreational pot in 2016.

“You’re talking about cash businesses that are in the hundreds of millions and approaching billions of dollars in state markets,” said Leslie Bocskor, founder of Electrum Partners, a marijuana consulting firm in Las Vegas. “And that’s just frightening from a community’s safety perspective.”

The issue is gaining some traction on Capitol Hill. Last week, seven senators — including Patty Murray, D-Wash., and presidential candidate Rand Paul, R-Ky., introduced a bill that would allow state-sanctioned marijuana businesses to use banking services without prosecution.

While Paul has been busy courting legalization backers as part of his presidential campaign, it was the first time that Murray has lent her name to a pro-marijuana bill since joining the Senate in 1993.

“Patty is real emblematic of the momentum that’s been building,” said Heck, one of 27 House members backing a bill called the Marijuana Businesses Access to Banking Act of 2015. “She’s been pretty deliberative about getting there but, to her great credit, she did.”

‘Clarity and security’

Murray said in a statement that she wanted to give “much-needed clarity and security” to banks, credit unions and marijuana businesses.

Bocskor said many investors are eager to capitalize on marijuana companies if they can be made confident that their investments will be safe. His company is exploring alternatives, including the use of foreign banks — he noted, for example, that pot establishments in the marijuana haven of Amsterdam already accept credit cards. And he said it’s possible that outside firms could sign agreements to operate banks on Indian reservations, taking advantage of their tribal sovereignty.

“We believe there are advantages in it,” said Bocskor. “We would like to see Native Americans be able to use banking as another method to bring a little more economic development to the tribal lands. That can happen, but it’s a pretty heavy lift.”

Scott Jarvis, director of Washington state’s Department of Financial Institutions, questioned whether such a system would work, saying tribes would still end up “with a whole bunch of money that they have to get somehow to the real world system.”

In Washington state, Jarvis said that nearly a dozen state-chartered banks and credit unions are now working with marijuana businesses.

“They’re pretty quiet about it,” he said. “Nobody wants to be known as a marijuana bank.”