What happens when a state law contradicts a U.S. federal law?

The law that applies to situations where state and federal laws disagree is called the supremacy clause, which is part of article VI of the Constitution [source: FindLaw]. The supremacy cause contains what's known as the doctrine of pre-emption, which says that the federal government wins in the case of conflicting legislation. Basically, if a federal and state law contradict, then when you're in the state you can follow the state law, but the fed can decide to stop you.

The operative term here, though, is "can."

Arizona's immigration law is a great example of the federal government fully enforcing the supremacy clause. When Arizona passed a very strict immigration law, the federal Justice Department sued them to overturn it under the supremacy clause. A spokesman from the Obama administration stated that the reason it went after Arizona is that the state law had international implications, especially in Mexico and the rest of Latin America. Proponents of the Arizona law said that the state was just enforcing federal law, since the feds would not do it and illegal immigrants were costing Arizona a lot of money. The case went all the way to the U.S. Supreme Court, where the Court overturned parts of the law and upheld others [source: Cohen]. Nevertheless, officials at the Department of Homeland Security said due to limited resources, it was not likely to step into illegal immigrant cases except high priority ones like those involving felonies [sources: Archibold, Cohen].

Historically, the federal government has not cracked down every single time a state and federal law contradict. If state law contradicts federal law but it's not something that affects national security or international relations, the fed might not intervene. In Nevada, certain counties have legalized prostitution, which also violates federal law, but the federal government has so far not enforced the doctrine of pre-emption in Nevada. Prostitution is illegal according to U.S. federal law, but under Nevada state law, counties with a population of less than 700,000 people can legally have legal brothels [source: Tan]. Unlike in Arizona, the federal government has not sued the state to shut down prostitution, and unlike California's medical marijuana dispensaries, the fed has not raided any brothels in the state. You could argue that prostitution is also an international issue, since human trafficking is certainly a problem that crosses state and national borders, but the federal government has not taken any action in Nevada.

Probably the best litmus test for how the federal government will handle marijuana legalization in Colorado and Washington is to look at how it's handled legalized medical marijuana in other states.

As we saw earlier, the federal government can enforce the doctrine of pre-emption, but it doesn't exercise its full power in every case. In California, where medical marijuana is legal, the federal government has taken a different tack.

California legalized medical marijuana in 2003, and the state's marijuana facilities have had a rocky relationship with the federal government, especially beginning in the fall of 2011 [sources: NORML, Rondoni]. Dispensaries in California have been subject to federal raids, though in most cases there haven't been any arrests -- instead, the government seizes and destroys the business owner's plants and sometimes shuts the businesses down completely [source: Ifill].

In an interesting twist, the city of Oakland, Calif. sued the federal government for trying to close the largest medical marijuana facility in the country (which happens to be based in Oakland) [source: Romney]. This case is still unresolved, but if Oakland wins, it could set a precedent protecting California's medical marijuana businesses from federal raids [source: Rondoni].

In Colorado, dispensaries and other medical marijuana businesses have been subject to raids and audits conducted under federal law [source: Chun].

If the federal government's recent treatment of medical marijuana facilities is any indication, Colorado's and Washington's marijuana businesses can expect some legal trouble. When it comes to full-on marijuana legalization in Colorado and Washington, the DEA isn't sure what it's going to do yet. Both new laws will be effect by early 2013 and both states have asked the U.S. Dept. of Justice for guidance where the state laws conflict with federal drug law [source: Associated Press]. In Dec. 2012, President Barack Obama stated that the federal government won't go after recreational marijuana users in these states due to limited resources. But the Dept. of Justice is waiting to see what regulations the two states adopt for implementing the ballot initiatives before taking any action [source: Yost].

One big difference between medical marijuana and outright legalization is that there's more of an opportunity for big business to get involved. There are rumors that big tobacco companies like Philip Morris have already snatched up warehouse space in Colorado (though the company denies it) [source: Dokoupil]. This wouldn't be the first time that Philip Morris tried to get in on the pot business. Back in 1993, France was considering legalization, and the company reserved a trademark for the brand name "Marley" [source: NPR]. If big business backs marijuana legalization, it could be potentially game-changing, since unlike small-scale growers and producers, a company like Philip Morris has the money and lobbying power to influence politicians on a federal level.