Loss of citizenship (INA § 349, 8 USC § 1481)
Section 349 of the INA [8 USC § 1481] specifies several conditions under which US citizenship may be lost. These include:
becoming a naturalized citizen of another country, or declaring allegiance to another country, after reaching age 18;
serving as an officer in a foreign country's military service, or serving in the armed forces of a country which is engaged in hostilities against the US;
working for a foreign government (e.g., in political office or as a civil servant);
formally renouncing one's US citizenship before duly authorized US officials; or
committing treason against, or attempting or conspiring to overthrow the government of, the US.