The idea of subjecting U.S. citizens to the whims of foreign courts is so antithetical to U.S. lawmakers that for 15 years Washington has opposed participation in the International Criminal Court (ICC), which tries defendants accused of war crimes, crimes against humanity and genocide. But the International Megan’s Law was unanimously adopted by the House on Feb. 1 by a voice vote after just 40 minutes of floor debate. In December, it cleared the Senate with Sen. Corker’s passport amendment by unanimous consent. Not a single lawmaker has gone on record opposing the bill.

A handful of states already have statutes identifying registered sex offenders on their driver’s licenses. But legal experts say H.R. 515 represents the first time in U.S. history that American citizens would be subject to such a requirement by federal law. Critics have compared the required passport identifier to the Scarlet Letter worn by Nathaniel Hawthorne’s protagonist for the sin of adultery. The bill earmarks $6 million a year to help fund a new federal agency called the “Angel Watch Center” with broad powers to compile and share information domestically and globally about registered sex offenders.

The law applies only to ex-offenders who have been convicted of sex crimes involving minors (people who rape adults are apparently free to travel at will), and is ostensibly designed to make it harder for active offenders who “[plan] their trips around locations where the most vulnerable children can be found … [using] the anonymity provided by foreign travel to help hide their hideous crimes,” in the words of Rep. Ann Wagner (R-MO), a cosponsor of the legislation.

Most incredibly, an amendment added to the bill in December by Sen. Bob Corker (R-TN) requires that qualifying ex-offenders have a “visual designation affixed to a conspicuous location” on their passports. Any travel documents that were issued prior to the law’s passage would be subject to revocation by the Department of State.

The bill’s supporters say it is designed to prevent the practice of “sex tourism.” In practice, it amends federal law to require registered sex offenders to provide information about any intended travel outside the United States — including travel dates and itinerary — and provides for that information to be shared with the governments of any countries they plan to visit. Failure to comply with the notification requirement would be punishable by fines and up to 10 years in prison.

Now, a bill that passed Congress last week and is now awaiting a signature from President Barack Obama risks gambling away the civil rights of thousands of law-abiding Americans each year by subjecting them to heightened scrutiny not just at home but abroad. The legislation ( H.R. 515 ) was sponsored by Rep. Christopher Smith (R-N.J.) and bears the laborious title : “The International Megan’s Law to Prevent Child Exploitation and Other Sexual Crimes Through Advanced Notification of Traveling Sex Offenders.”

Ex-offenders convicted of sex crimes in the United States are accustomed to facing numerous and often burdensome restrictions. There are laws governing where they are allowed to live, what kind of job they can hold and, in some cases, if they are even allowed to own a computer, long after they have ostensibly paid their debt to society.

The types of crime it purports to address are horrendous. Exactly how often they occur, though, is hard to say. In published testimony, the Department of Homeland Security (DHS) has credited Operation Angel Watch, the precursor program that inspired the Angel Watch Center in H.R. 515, with providing “1,700 leads” about sex offenders “to nearly 100 countries” in 2013. But the agency doesn’t (and presumably couldn’t) know how many of those leads disrupted actual attempts at child abuse. The program is part of a larger DHS initiative targeting international sex crimes dubbed “Operation Predator” that the agency boasts has led to 14,000 arrests since 2003. However, according to a summary of that program published in 2012, only 99 arrests over the prior decade involved “traveling sex offenders,” with the majority netting purveyors of child pornography.

In any case, individuals convicted of traveling overseas to have sex with minors, or attempting to do so, are already barred (appropriately) from having a passport under federal law. The Supreme Court has ruled that the right to travel — both domestically and internationally — is protected by the Constitution. In the 1960s, the court invalidated a law that prohibited a member of a Communist organization from attempting to use or obtain a passport as a violation of the Fifth Amendment, and has promised it “will construe narrowly all delegated powers that curtail or dilute citizens’ ability to travel.” In a 1981 case validating a law that placed passport restrictions on individuals who owe back child support, the court clarified this boundary by saying the government has the authority to restrict the movements of certain criminal offenders if it can show a “rational basis” for the restriction. In addition to those who owe child support, the Department of State currently denies passports to people who have been convicted of certain drug felonies while they are on supervised release; and the government recently announced it will begin revoking the passports of individuals who are in arrears more than $50,000 in taxes.

However, in each of these cases, the passport ban is only in effect until the individual in question has settled their legal issues. The International Megan’s Law casts an inappropriately wide net and places unnecessary and burdensome scrutiny on classes of ex-offenders who pose no risk of abusing minors overseas or were convicted of their crimes decades ago and may be traveling as a necessary component of their employment.

Meanwhile, state sex offender registries have become so broad in their application that they’re practically useless. According to the National Center for Missing & Exploited Children there are 843,680 registered sex offenders in the U.S. With few exceptions it is impossible to discern genuine risk from a public sex offender database, where “sex crimes against minors” can include everything from outright rape to teenagers texting nude photos to each other, or a 20 year old having sexual intercourse with her 16-year-old boyfriend (a category that is made even more complex by variations in state law governing the age of consent).

The International Megan’s Law will facilitate preemptive action against all of these ex-offenders — without considering the specifics of their crimes — with the intent enabling officials of foreign countries to take “actions that they deem appropriate to ensure public safety,” as the Government Accountability Office put it in a 2013 report. At best, this will involve denying qualifying offenders entry into their country of destination. At worst, the law will subject U.S. nationals to surveillance, harassment and entrapment by foreign law enforcement agencies with questionable justice systems.

On paper, at least, this means that if the president signs H.R. 515 into law he will be paving the way for American citizens to be arrested, interrogated, prosecuted and possibly convicted in foreign jurisdictions without the benefit of due process on the basis of wobbly intelligence provided by the U.S. government. The White House has yet to comment on whether the president will veto H.R. 515. At least one criminal justice advocacy group has threatened to sue the government if the bill becomes law, saying it believes the law to be unconstitutional.

For their part, the sponsors of H.R. 515 say their bill is consistent with Congress’ authority to “regulate commerce with foreign nations.” They may be right, given that the law would rely on foreign powers to do its actual dirty work.

But with courts in a number of states now considering the constitutional implications of overly restrictive sex offender laws, signing a new federal statute increasing those restrictions in a way that will put Americans at risk while traveling abroad would be a stain on the Obama legacy that the president can do without.