PHOENIX—Arizona officials are taking the state's own medical marijuana law to court.

Attorney General Tom Horne late Friday sued the U.S. Justice Department and other defendants on behalf of the state and Gov. Jan Brewer.

The suit asks a federal judge to rule on whether strict compliance with the Arizona law provides protection from federal prosecution or whether the Arizona measure is pre-empted by federal law.

The state law approved by voters in November, like those in other states, decriminalizes distribution, possession and use of marijuana for medical purposes under specified circumstances.

However, the U.S. attorney for Arizona has reminded state officials that marijuana remains illegal under federal law.

Horne said the Arizona suit was intended get a court ruling "that makes it clear what direction we can safely go -- either to implement the law or that we cannot."

The suit also named medical marijuana supporters, a group representing would-be dispensary operators and others as defendants in the case. Horne said they accepted invitations to be included in the case to ensure the state law gets a vigorous defense.

Brewer announced the planned lawsuit Tuesday, saying she's concerned that state employees could face federal prosecution for regulating the state program.

The governor and Horne, both Republicans, opposed the medical marijuana law but said they weren't trying to thwart the will of the voters. They said the lawsuit is specifically prompted by a May 2 letter in which U.S. Attorney Dennis Burke noted that marijuana remains illegal under federal law and that criminal prosecutors of traffickers and others are possible.

Burke's letter did not specifically mention state employees, but he said his office intends to prosecute individuals and organizations engaged in illegal manufacturing, distribution and marketing involving marijuana.

Burke did not immediately respond to a request for comment Friday, but he told The Arizona Republic there had been no policy change.

"We have no intention of targeting or going after people who are implementing or who are in compliance with state law," Burke told the newspaper. "But at the same time, they can't be under the impression that they have immunity, amnesty or safe haven."

Horne said Burke's letter and similar letters sent by U.S. attorneys elsewhere raised the prospect of federal prosecutions related to medical marijuana, and he noted that a letter signed by U.S. attorneys in Washington state said state employees administering a medical marijuana program would not be immune from liability under a federal drug law.

Saying she was worried about federal prosecution of state workers, Washington Gov. Chris Gregoire vetoed key parts of a legislative measure to clarify her state's medical marijuana law.

Elsewhere, Rhode Island Gov. Lincoln Chafee has suspended plans to license three medical marijuana dispensaries after a U.S. attorney warned the dispensaries could be prosecuted for violating federal law.

In Montana, two medical marijuana providers sued the Justice Department on May 10 to challenge March 14 raids of their businesses. The lawsuit claimed the raids exceeded the federal government's authority, pre-empted Montana's medical marijuana law and violated the providers' civil rights.

A spokesman for a Washington-based medical marijuana advocacy group said the Arizona lawsuit won't accomplish anything because it won't change federal law or enforcement policies and because individual patients can grow their own marijuana.

"Gov. Jan Brewer is trying to hamstring this program," said Morgan Fox of the Marijuana Policy Project.

Between April 14 and Tuesday, Arizona approved 3,696 applications for patients to have and use medical marijuana, including 2,694 for growing up to 12 plants each. An additional 69 applications have been approved for caregivers, who can provide marijuana for up five patients other than themselves.

An application period for dispensaries is supposed to begin Wednesday, but Brewer is expected to direct the Department of Health Services to not proceed with that part of the program.

M. Ryan Hurley, a Scottsdale lawyer for would-be dispensary operators, said they're troubled because the state is not proceeding with full implementation of the law.

"They've invested a lot of time and effort and money in this process in reliance of the law," he said.

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