From the Washington Post editorial board:
The most powerful non-military tool the United States possesses is exclusion from its banking system. Mr. Obama should make clear that if Russia does not retreat from Ukraine, it will expose itself to this sanction, which could sink its financial system. Russia’s economy, unlike that of the Soviet Union, is heavily dependent on Western trade and investment. It must be made clear to the Kremlin that the Ukraine invasion will put that at risk.
I'm no expert on the banking sector, so I have trouble following exactly what excluding Russia from the U.S. banking system would mean. However, I do wonder whether whatever it does mean would be consistent with U.S. GATS commitments.