The NATO Shield Act requires the President to consult with Congress within 72 hours before taking any action to withdraw the United States from NATO, and to submit a detailed report within 48 hours of initiating a withdrawal that includes legal justification, strategic reasoning, and expected military effects. Any withdrawal action automatically terminates after 30 days unless Congress passes a joint resolution approving it, and Congress can also pass a joint resolution during that 30-day window to stop the withdrawal entirely. The bill establishes expedited procedures for Congress to vote on these resolutions, with strict timelines ensuring the Foreign Affairs committees report within 12 days and full chamber votes occur within 3 days of reporting. The legislation applies to any formal or informal step toward NATO withdrawal, and Members of Congress can sue in federal court if the President violates these requirements, with courts required to expedite such cases. This bill essentially gives Congress a veto power over NATO withdrawal by requiring congressional approval for any such action to remain in effect beyond 30 days.