Aptheker v. Secretary of States (1964) overturned a law allowing the state
department to deny passports to American Communists because it violated the
First Amendment.

Haig v. Agee (1981) raised and answered First Amendment questions regarding
the right to travel in order to prevent speech deemed harmful to national
security.

Zemel v. Rusk (1965) refused to interpret the First Amendment so as to
grant a citizen an absolute right of travel to other countries to assess
the effects of U.S. policies abroad.