 The provision calling for loss of citizenship for foreign military service was held by the Supreme Court not to be enforceable without proof that said service had been voluntary, in a 1958 case ("Nishikawa v. Dulles"), and revocation of citizenship as a punishment for desertion was struck down that same year in another case ("Trop v. Dulles").However, in yet another 1958 case ("Perez v. Brownell)," the Supreme Court affirmed the provision revoking the citizenship of any American who had voted in an election in a foreign country, as a legitimate exercise (under the Constitution's Necessary and Proper Clause) of Congress' authority to regulate foreign affairs and avoid potentially embarrassing diplomatic situations.Associate Justice Felix Frankfurter, the author of the opinion of the Court (supported by a 5–4 majority), wrote that