SAN FRANCSICO (KCBS)— Now that four states have legalized recreational marijuana use, entrepreneurs want to start businesses. It may be a lucrative proposition, but there’s no place to keep the money.

With federal law still banning the possession and use of marijuana, federally regulated banks have closed marijuana-related accounts. That’s leaving business owners holding the bag, which is filled with cash. They’re trying to cope in various ways.

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Peter Conti-Brown, an academic fellow and banking expert at Stanford Law School said the issue treads some pretty uncertain regulatory terrain. He says we’re seeing some formal chartering of new financial institutions that are coming into existence for precisely this purpose.

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“It’s kind of [like] stuffing cash under your mattress and trying to exist as legitimate businesses outside of the financial system,” he said.

It’s one thing to try and run a mom and pop business this way, but with the potential for multi-million dollar enterprises, it’s a different story.

“Without the ability to clear checks through interstate financial institutions or participate in the payment systems generally, there’s not much you can do by way of growth,” he said.

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Brown agreed that we’re seeing more of these legitimate businesses under state law pushing for more federal recognition.