A Department of Homeland Security police officer stands watch at a security checkpoint at Hartsfield–Jackson Atlanta International Airport.

Lawmakers were introducing legislation this week tightening the program that allows millions to travel to the United States without a visa, as Congress moves to enhance security following the deadly Paris attacks.

“Now we’re looking at the Visa Waiver Program, those gaps and vulnerabilities in that,” number two House Republican Kevin McCarthy told CNN Wednesday.

“You’ll see it roll out tomorrow” in the House of Representatives, he added on Fox, adding that it would be introduced on the floor of the chamber next week.

The visa waiver program is available to citizens of 38 countries, largely U.S. allies and relatively stable developed democracies. Many are in Europe.

Twenty million visitors annually use the program, which allows them to stay in country for 90 days and provides a boon to the U.S. economy.

McCarthy said a key component would be restricting travelers who had been to Iraq or Syria, where Islamic State extremists have drawn thousands of foreign fighters.

“Anyone who’s traveled to Iraq or Syria in the last five years should not be able to just do the online (application) and come to America,” he said.

Senators introduced bipartisan legislation Tuesday aimed at preventing terrorists from abusing the program.

The tourism sector is worried that imposing new procedures will discourage travel.

The visa-free privilege enjoyed by most European countries including France means they fill out a detailed form online and pay a small fee, rather than apply at U.S. consulates.

Their biographical details are cross-referenced with various security databases before they board a U.S.-bound flight.

Weeks after the Paris attacks, the White House announced its own enhancements Monday, including capturing data on a visitor’s travel to any country “constituting a terrorist safe haven,” and calling for greater intelligence sharing with participating countries.

Senators including Democrat Dianne Feinstein want to go further, adding into their legislation a requirement that visitors also submit fingerprints and photographs prior to travel.

Today, fingerprints and photos of visa-free travelers are taken upon U.S. arrival.

Imposing the new regulations could sabotage spontaneous U.S. tourism, warned Jonathan Grella, executive vice president of the U.S. Travel Association, who said the additional biometric requirements might be a “poison pill” in the legislation.

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