The Internal Revenue Service has opened an audit of a Denver medical-marijuana dispensary, the latest action in what one observer calls a "guerrilla campaign" by the federal government to push back against the cannabis industry. The Internal Revenue Service has opened an audit of a Denver medical-marijuana dispensary, the latest action in what one observer calls a "guerrilla campaign" by the federal government to push back against the cannabis industry.

The audit is believed to be the first of its kind in Colorado and follows audits of numerous medical-marijuana dispensaries in California and other states.

Investigators are examining whether it was unlawful for the dispensaries — which are illegal enterprises under federal law — to deduct business expenses from their federal taxes, said Jim Marty, a Denver accountant who represents the Colorado dispensary.

Marty declined to name the dispensary or say where it is located. Marty said the dispensary was notified of the audit earlier this month.

"So far," he said, "the IRS has been pretty cooperative. . . . The client had good records."

Marty said he expects the IRS to look broadly at dispensaries in Colorado. If so, that would mirror what the agency has done in California, where tax attorney Henry Wykowski said the IRS has undertaken at least 30 audits of dispensaries.

The audits are also part of a bigger series of events in which the federal government appears to be more actively asserting itself in state-legal marijuana businesses.

In recent months, U.S. attorneys in Washington state and California have sent letters to state officials there warning them that efforts to regulate medical-marijuana businesses will not change the federal government's disapproval of those businesses.

In one letter, U.S. attorneys in Washington warn Gov. Christine Gregoire that state employees who regulate the businesses "would not be immune from liability."