Washington Initiative I-502 is not above federal law. In this letter written by the Department of Justice, it is made clear what will happen should I-502 pass at the ballot:
The Washington legislative proposals will create a licensing scheme that permits large-scale marijuana cultivation and distribution. This would authorize conduct contrary to federal law and thus, would undermine the federal government’s efforts to regulate the possession, manufacturing, and trafficking of controlled substances. Accordingly, the Department could consider civil and criminal legal remedies regarding those who set up marijuana growing facilities and dispensaries as they will be doing so in violation of federal law. Others who knowingly facilitate the actions of the licensees, including property owners, landlords, and financiers should also know that their conduct violates federal law. In addition, state employees who conducted activities mandated by the Washington legislative proposals would not be immune from liability under the CSA. Potential actions the Department could consider include injunctive actions to prevent cultivation and distribution of marijuana and other association violations of the CSA; civil fines; criminal prosecution; and the forfeiture of any property used to facilitate the violation of the CSA. As the Attorney General has repeatedly stated, the Department of Justice remains firmly committed to enforcing the CSA in all states.