President Biden has followed President Trump’s lead in attempting to use international travel bans to reduce the spread of Covid-19. But Mr. Biden is reportedly considering an expansion of the policy. U.S. citizens, permanent residents and their immediate relatives are all exempt from existing travel bans.

The Washington Post reports the administration is considering a mandatory seven-day quarantine for everyone arriving from abroad—regardless of citizenship, vaccination or a negative Covid test. Some observers have urged...

Passengers check in for their flight at O'Hare International Airport in Chicago, Nov. 24.

Photo: tannen maury/Shutterstock

President Biden has followed President Trump’s lead in attempting to use international travel bans to reduce the spread of Covid-19. But Mr. Biden is reportedly considering an expansion of the policy. U.S. citizens, permanent residents and their immediate relatives are all exempt from existing travel bans.

The Washington Post reports the administration is considering a mandatory seven-day quarantine for everyone arriving from abroad—regardless of citizenship, vaccination or a negative Covid test. Some observers have urged officials to go further and ban entry by unvaccinated citizens or by citizens returning from high-risk countries.

The government has the authority to impose reasonable health inspections at the border. But these measures would go further than anything that has ever been done. They raise significant constitutional questions.

The right to enter their country is an essential element of citizenship. In 1215 the Magna Carta proclaimed: “It shall be lawful for any man to leave and return to our kingdom.” In the 20th century, the Supreme Court declared that “the right to travel is part of the ‘liberty’ of which the citizen cannot be deprived without due process of law under the Fifth Amendment. . . . Freedom of movement is basic in our scheme of values.”

The right to re-enter can be subject to reasonable restrictions, including passport requirements and health inspections. Existing law gives the federal government the authority to isolate or quarantine citizens arriving from abroad, but only under narrow circumstances. Federal regulations limit quarantine and isolation to cases in which the individual is known to have been exposed to a communicable disease. Everyone subject to such measures must be provided with “an explanation of the factual basis” for the Centers for Disease Control and Prevention’s belief that he had been exposed or infected.

The existing regulations apply to all arrivals to the U.S. For citizens, the Constitution provides an added protection against blanket restrictions on entry. Universal quarantine requirements for citizens, such as the White House is reportedly considering, aren’t based on any particular risk assessment. To the extent they apply to citizens with multiple negative tests, they go beyond what is permitted by existing regulations, while failing to tailor the burden on constitutional rights in any reasonable way.

It is no answer to say that Covid is somehow different. The existing federal quarantine rules were applied to some of the worst known viruses, like Ebola and SARS.

A quarantine isn’t a banishment, but it can become one. Early in the pandemic, Australia imposed rigid entry requirements on citizens—a mandatory two-week quarantine and a tight limit on total arrivals. Many Australians were stranded outside their country for months. Such a situation is no longer a dystopian fantasy for Western countries, so it’s important to draw constitutional lines early.

A suspicionless quarantine requirement, especially as applied to citizens, erodes basic rights. The government could take many lesser steps, from limiting flights from high-risk places to imposing rigid testing requirements. But a universal quarantine is unreasonable. It would burden even vaccinated citizens coming from places with less infection than the U.S.

Restricting citizens’ ability to travel is a hallmark of a police state. Infectious disease will always be with us. It cannot become an excuse to give the federal government carte blanche to control the lives of citizens.

Mr. Kontorovich teaches constitutional law at George Mason University Scalia Law School.

Wonder Land: What we needed most from the Government during Covid's two long years were mid-course corrections. Instead politicians chose rigidity, such as Joe Biden's vaccine mandate. Images: AFP via Getty Images Composite: Mark Kelly The Wall Street Journal Interactive Edition