In Zemel v. Rusk, the U.S Supreme Court upheld the constitutionality of a law that restricted travel to certain countries deemed dangerous by the Secretary of State. The plaintiff, Carl Zemel, had sought validation for his passport to allow him to travel to Cuba but was denied due to regulations imposed under the Passport Act of 1926 and President Kennedy's Proclamation 3447 which declared an embargo on trade with Cuba. He argued this violated his Fifth Amendment right as it deprived him liberty without due process and also infringed upon his First Amendment rights by limiting freedom of speech and inquiry through restriction on travel. However, in a majority decision led by Justice Potter Stewart, the court ruled that these restrictions were within Congress’s power over foreign affairs and did not violate any constitutional rights because they were based on valid national security concerns rather than suppression of ideas.

In the dissenting opinion for Zemel v. Rusk, Justice William O. Douglas argued that the Secretary of State's refusal to validate passports for travel to Cuba was an unconstitutional infringement on citizens' right to travel and receive information. He contended that this restriction was not a necessary measure in protecting national security or foreign policy interests but rather served as a form of censorship by limiting Americans' access to firsthand knowledge about Cuba. Furthermore, he asserted that it is not within the power of the executive branch alone to impose such restrictions without explicit authorization from Congress; doing so violates separation-of-powers principles enshrined in the Constitution.