HELENA — The president of an advocacy group behind a lawsuit and a ballot measure challenging Montana's restrictive new medical marijuana law plans to plead guilty to a federal drug charge related to the 2011 raids on pot providers across the state.

Chris Lindsey is a co-founder of the now-defunct Montana Cannabis, one of the largest providers raided in the March 2011 crackdown on large medical marijuana operators in the state. More than two dozen people have been indicted or sentenced on various charges, from drug manufacturing to money laundering, since the raids.

Lindsey has struck a deal with federal prosecutors to plead guilty to conspiracy to maintain a drug-involved premises. The charge carries a penalty of up to 20 years in prison and a $500,000 fine upon conviction.

The plea agreement, which was filed on Friday, drops several other charges, including conspiracy to manufacture and distribute marijuana and possession of a firearm during a drug-trafficking offense.

Lindsey did not return a call for comment on Tuesday.

He will appear in court on Sept. 6, the same date that his former partner, Tom Daubert, is to be sentenced on the same charge.

Lindsey is the public face of the Montana Cannabis Industry Association, which has fought hard against a 2011 law that banned medical marijuana providers from making a profit and restricted who could qualify as a registered user.

The association's lawsuit led a judge to block portions of the new law, including the profits ban, while the litigation is pending. The Montana Supreme Court is weighing whether to keep the district judge's injunction in place.

An association-backed referendum asking voters to repeal the 2011 law will appear on the Nov. 6 ballot.

Daubert made a plea deal earlier this year and is asking a judge for a sentence of probation with community service. Federal prosecutors are recommending a prison sentence between 6 1/2 and eight years.

Another Montana Cannabis partner, Richard Flor, was sentenced earlier this year to five years in prison. A fourth partner, Chris Williams, is still fighting the federal charges, as is Dan Nichols, a former Montana Cannabis employee who is known for kidnapping a world-class biathlete in the 1980s with his father in a scheme to make the woman his mountain bride.

Williams and Nichols are scheduled to go to trial on Sept. 24