The issue seems to be coming up more and more often: state law conflicting with federal regulations. As a Federal Firearms Licensee (FFL), it is important for you to know what to do when you run into a conflict.
When state laws give people more rights than federal law, legally, the state should prevail. You see this happening in cases of medical marijuana, recreational marijuana, immigration, etc. However, state law does not always prevail. The supremacy clause, which is part of article VI in the Constitution, contains the doctrine of pre-emption. This means that when you are in the state, you can follow the state law, but the federal government can choose to stop you.
As an FFL, you must follow federal law. In 2011, the ATF issued an Open Letter which spelled it out. This Open Letter reminded FFLs that because the license to transact firearms is under the authority of the federal government, you must follow federal law when you transfer firearms or ammunition.
For example, even though your state may have legalized medicinal or recreational marijuana, it is considered a controlled substance under federal law. As the ATF Open Letter explains it, any person using marijuana for any purpose is an unlawful user of a controlled substance and is prohibited by federal law from possessing firearms or ammunition. The revised ATF Form 4473 is clear: “The use or possession of marijuana remains unlawful under Federal law regardless of whether it has been legalized or decriminalized for medicinal or recreational purposes in the state where you reside.”