Marijuana opponents in Colorado are using a recent U.S. Supreme Court ruling to gird a new argument against making pot legal.

They're not talking about the landmark health-care ruling. They're talking about last week's Arizona immigration ruling in which the court reiterated that states can't buck the federal government.

That line has marijuana-legalization opponents in Colorado warning that the same would apply to states that legalize pot. They argue that states would only set themselves for pricey legal battles with no chance for success against a federal drug law that considers marijuana illegal in all circumstances.

Marijuana legalization supporters point out that Colorado and 15 other states are already in direct violation of federal drug law for allowing the use of pot for certain medical conditions.