Local sheriff's deputies and U.S. Drug Enforcement Administration agents disagreed when they converged on Diane Monson's house in Oroville, Calif., two years ago.
The county cops accepted Monson's explanation for growing six marijuana plants: She had a doctor's permission to smoke it for back pain, so the pot was legal under the state's 1996 "medical marijuana" law.
Diane Monson, who uses marijuana for her back pain, sued after federal agents seized plants in 2002 from her Oroville, Calif., home.
(Rich Pedroncelli -- AP)
But the DEA agents insisted that growing marijuana is still against federal law. They seized the plants and destroyed them.
Today that federal-state clash continues at the Supreme Court, where the justices will hear oral arguments on whether the Constitution permits the federal government to take action against those who use homegrown marijuana for medicinal reasons within states where it is legal to do so.
The case is the third medical pot case to reach the Supreme Court since voters overwhelmingly approved California's Compassionate Use Act. But the legal issues this time give the case importance well beyond the 11 states, mostly in the West, that since 1996 have eased or eliminated penalties for medical use of marijuana.
Among these states is Maryland, which last year set a maximum fine of $100 for medical users of less than an ounce of pot.
It has wider implications because Monson claims that federal drug busts of people such as her exceed Washington's authority under the commerce clause of the Constitution, which gives Congress the power to regulate trade "among the several states."
Last year, the San Francisco-based U.S. Court of Appeals for the 9th Circuit ruled 2 to 1 that Monson was right. If the Supreme Court agrees, it could limit the federal government's power over not just the cultivation and use of marijuana, but also other activities.
Much modern government regulation exists because the Supreme Court articulated a broad definition of interstate commerce during the 20th century. This permitted the court to uphold, as exercises of Congress's commerce clause power, a wide range of national laws -- from the economic policies of the New Deal to the civil rights era ban on racial segregation in hotels and restaurants.
Perhaps the key ruling came in 1942, when the court held that the Roosevelt administration could enforce acreage controls against an Ohio wheat farmer who claimed his crop was entirely for his own use.
The court said that even subsistence farming could change the overall supply and price of grain; this "substantial effect on interstate commerce" triggered Congress's authority.
But in more recent years, the court has tightened its definition of interstate commerce.
In 1995, the court struck down a federal ban on gun possession within 1,000 feet of a school, ruling that Congress's claims that school gun violence had a "substantial effect" on the economy were implausible.
And in 2000, the court struck down a federal law giving women a right to sue rapists in federal court, ruling that such violence was not, "in any sense of the phrase, economic activity."