With its “Burma law, ” Massachusetts joined a procurement boycott of companies doing business in Burma. In Crosby v. NFTC, the U.S. Supreme Court held that Congress preempted the Massachusetts law, even though Congress was silent on preemption. The Court relied on actions by executive-branch, foreign, and corporate actors to find that the state law was an obstacle to implied objectives of federal Burma sanctions. In doing so, the Court diffused congressional accountability for preemption and constrained the “constituent diplomacy” by which states and local governments use their purchasing power to influence national policy and multinational corporations. Crosby shifted the burden to Congress to express its intent not to preempt such measures. Congress has several opportunities to meet this burden if it wants to preserve the diversity and balance that constituent diplomacy brings to the federal system.