The marijuana regulation law that Colorado Gov. John Hickenlooper signed last month includes a quarter-ounce limit on pot purchases by visitors from other states. Colorado residents, by contrast, may buy up to an ounce at a time. As I have mentioned before, making the purchase limit hinge on residency seems inconsistent with Amendment 64, the marijuana legalization initiative that is now part of Colorado's constitution. The quarter-ounce rule may also be vulnerable to challenge under the U.S. Constitution, since it discriminates against residents of other states.

Amendment 64 decriminalizes purchase and possession of up to an ounce by anyone who is 21 or older, without regard to residency. The fact that the initiative does not distinguish between Coloradans and residents of other states was one reason the legislature decided to let visitors buy marijuana, despite fears about the possible negative consequences of "pot tourism." Furthermore, Amendment 64 specifies that the state "shall not require a consumer to provide a retail marijuana store with personal information other than government-issued identification to determine the consumer's age, and retail marijuana stores shall not be required to acquire and record information about consumers other than information typically acquired in a financial transaction conducted at a retail liquor store." Yet Colorado's new marijuana law makes it a Class 2 misdemeanor, punishable by up to a year in jail and a $500 fine, to "sell a more than a quarter of an ounce…during a single transaction to a person who does not have a valid identification card showing that the person is a resident of the state of Colorado." That rule seems tantamount to demanding that stores acquire information about the locations of customers' homes, a requirement that Amendment 64 does not allow. Granted, the "government-issued identification" used by customers as proof of age will typically be a driver's license that reveals where they live. But under Amendment 64 customers could use a passport instead. The new law compels them to present IDs that include their addresses if they want to buy more than a quarter of an ounce. That requirement raises the possibility of a challenge under the state constitution.

In a new paper, Samford University law professor Brannon Denning notes that Colorado's residency-based purchase limit could be challenged under the U.S. Constitution as well. Article IV, Section 2, for example, says "the Citizens of each State shall be entitled to all Privileges and Immunities of Citizens in the several States." On its face, that guarantee seems inconsistent with Colorado's discrimination against nonresidents. But the Supreme Court has said the Privileges and Immunities Clause applies only to "fundamental rights," and Denning is skeptical that recreational marijuana use would qualify. (The Supreme Court has said another form of recreation, elk hunting, does not.) Medical marijuana use might carry more weight, Denning says, but Colorado still could defend its restriction by arguing that it bears a substantial relationship to a legitimate, nonprotectionist goal: avoiding conflict with other states and the federal government by making it harder to divert marijuana from Colorado into the interstate black market. The idea is that forcing nonresidents to buy pot a quarter ounce at a time instead of an ounce at a time will make it four times as difficult to amass quantities suitable for profitable smuggling.

Denning thinks a stronger challenge to the quarter-ounce rule could be made under the dormant Commerce Clause doctrine, which frowns upon laws that burden interstate commerce, especially when they explicitly discriminate against residents of other states. He notes that "nonresident pot tourists would be traveling in interstate commerce to purchase marijuana legally in Colorado." Furthermore, in Gonzales v. Raich, the 2005 decision upholding enforcement of the federal marijuana ban in states that allow medical use of the plant, the Court "concluded that the production and consumption of locally produced, noncommercial, medical marijuana…substantially affected the interstate marijuana market." If so, "state restrictions on the sale of marijuana to nonresidents…even though occurring within Colorado, would likely substantially affect interstate commerce," thereby triggering scrutiny under the dormant Commerce Clause doctrine.

Still, Denning says, the Court "has acknowledged that states can restrict trade for reasons other than securing commercial advantage for residents or for punishing those who reside elsewhere." Since Colorado's purchase limit is "intended to avoid interstate friction, not exacerbate it," he argues, "courts should grant the state some experimental leeway in the means it chooses to enforce its legitimate interests." He adds that Congress could explicitly authorize such experimentation, just as it gives states extra leeway in setting their own alcohol policies.

[Thanks to Glenn Reynolds for the link to Denning's paper.]