When so-called “pot shops” opened up legally in Colorado last week, one thing they couldn’t offer shoppers was the ability to pay via credit card.

Due to differences in state and federal law regarding marijuana’s legality as well as legal concerns of the banking industry, these groundbreaking businesses, which drew national attention and more than $5 million in sales in the past week, can’t use the federal banking system. Which means that they’re stuck doing business—everything from taking customer payments to paying employees—in cold, hard cash.

“There is absolutely no justifiable reason to allow this threat to public safety to continue in those states where the regulated sale of marijuana has been made legal,” Betty Aldworth, deputy director of the National Cannabis Industry Association (NCIA), said in a statement ahead of the launch of Colorado’s legal dispensaries.

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The problem at retail: For many of these businesses, the forced reliance on cash and storage of funds creates security concerns—partly because it drives a perception that the businesses have a significant amount of cash on hand at all times. “If we could remove the thought that we have a lot of cash on hand, perhaps it would re-instill some feeling of safety or security,” Toni Fox, the owner of Denver’s 3-D Cannabis Center, told TV station KWGN.

Different treatment? Cannabis industry groups note that the state of Colorado itself has access to the banking system, having deposited $9 million in medical marijuana sales tax funds in state-held bank accounts in the 2012-2013 fiscal year. That technically might be illegal under federal law. “Bankers holding accounts for a state with legal marijuana businesses but closing the accounts of those legal, regulated businesses are kidding themselves if they think they aren’t handling marijuana-related money,” the NCIA’s Aldworth told The Denver Post. State officials contend that even if the source of the money is considered illegal under federal law, the taxes collected are not.

All isn’t lost: In Washington, federal regulators and legislators are working on addressing the gaps between state and federal law. Rep. Ed Perlmutter (D-CO) has introduced a bill that would allow legal marijuana businesses access to banking. Meanwhile, the U.S. Justice Department is expected to clarify the legal issues involving federal banking, something the American Bankers Association welcomes. “There’s a great deal of guidance that banks would want to hear about in terms of banking with these types of businesses,” ABA Vice President of Compliance Richard Riese told the Wall Street Journal.

Denver’s show of support: Meanwhile, the Denver City Council passed a resolution Monday asking the federal government to give pot shops access to the federal banking system. “If it’s here, its regulation should be safe, responsible, and effective,” Councilman Chris Nevitt said of legalized marijuana sales, according to The Denver Post. “The piece that’s missing is banking.”

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