Tax season has begun, but for the cannabis-related businesses in the United States, difficulties lie ahead.

With four states now selling recreational marijuana, and 23 states and the District of Columbia offering medicinal marijuana, businesses and dispensaries face legal problems when they go to file their taxes.

Not only can it be especially difficult enough to get a marijuana business license in some areas, but the differences between federal and state laws make filing taxes a nightmare for some enterprises. After all, they are technically breaking a federal law when they send their tax documents to the Internal Revenue Service.

It’s a catch-22: business face tax evasion charges if they don’t report their earnings, but they could see criminal charges for selling the substance in the first place.

And then there’s the taxes themselves. Robert W. Wood, a contributor to Forbes, says that such businesses can expect to pay up to 50% in taxes this season.

Part of these high costs stem from the tax code itself. Section 280E states that even legal dispensaries can’t claim deductions because marijuana is still illegal at the national level, and the IRS has no choice but to enforce this law.

“I think it’s going to take a very long time for all the states to legalize cannabis; legalization will continue to be a state issue for another decade or two,” said Greg Tucker of Canna Advisors, a medical marijuana advisory company. “However, the federal government should look into a way to harness the taxing situation.”

There are, however, some exceptions to this code: medical marijuana dispensaries are distinct from marijuana businesses because they can deduct care-giving expenses — as long as at least 90% of their premises are used for other purposes besides dispensing marijuana.

All marijuana businesses also have to figure out their profits, based upon the cost of goods sold and the resale value. Adding in employee wages, marketing, and other expenses complicates how the taxes are filed, though.

Yet despite the tax troubles, marijuana businesses make up the fastest growing industry in the United States. If the trend spreads to all 50 states, it could surpass organic foods as the most profitable agricultural business in the country.

The State of Legal Marijuana Markets, an annual report published by the ArcView Group, predicts that the industry will see 32% growth in 2015 alone. In 2014, business increased by 74% to $2.7 billion, up from $1.5 billion in 2013.