Missouri may not let legal marijuana companies pay taxes in cash. That could be a problem.

Late Monday, the Missouri Department of Health and Senior Services issued a proposed rule governing the way licensed medical marijuana facilities should pay taxes and other money owed to state government.

The rule says that state-licensed companies that handle cannabis — for example, dispensaries or growing outfits — will be required to pay their Missouri taxes and fees “via any payment method normally acceptable to those agencies other than cash.”

That could be a problem. It’s not the way state-legalized cannabis companies have done business so far. Since the inception of medical marijuana in California in the 1990s, they’ve typically been all-cash operations.

Blame Uncle Sam for this state of affairs.

All banks face regulation from federal entities like the FDIC, the Office of the Comptroller of the Currency or the Federal Reserve, said Max Cook, president and CEO of the Missouri Bankers Association. By law, the feds can’t work with cannabis companies because federal law classes marijuana alongside illegal substances like heroin.

“The federal regulators can impose cease and desist orders, civil money penalties, etc.,” Cook said in an email to the News-Leader earlier this year. “These penalties can be in the millions. Bankers most often aren’t willing to take those risks.” [Read more at Springfield News Leader]