I am wondering about the laws of Dina d'malchuta dina in the United States when there is a contradiction between state and federal laws.
Case in point: In 2012 both Colorado and Washington passed state legislation that legalized the use of recreational marijuana. However, marijuana is still illegal under the federal Controlled Substance Act. Until recently1, the US Justice Department was still considering what policy to approach in such a discrepancy, which revolves around the ambiguously implied exo-constitutional powers stipulated in the 10th amendment2.
All of this makes me wonder about what the halacha would say. Disregarding the halachic issue of drug use, is it permissible to do something that's legalized in your state but illegal federally? What does the halacha say about state/federal conflicts of laws?
I'm not so familiar with current American state laws, otherwise I would have picked an example that is only halachically problematic because of its dina d'malcuta dina issue (and as has been answered previously, the issues of marijuana are broader than that).
1. As of August 29, 2013, Attorney General Eric Holder has authorized Washington and Colorado "to create a regime that would regulate and implement the ballot initiatives that legalized the use of marijuana for adults."
2. The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.