The U.S. travel industry is pushing back against the growing possibility that Congress could seek to restrict a program that allows millions of travelers to enter the United States without a visa, saying it could impede business and tourist travel.

The U.S. Travel Association is defending the Visa Waiver Program that allows some citizens from 38 countries to travel to the United States for business or leisure for up to 90 days without a tourist visa. A growing chorus of lawmakers, including House Homeland Security Chairman Michael McCaul (R-Texas), is calling to reexamine the program for potential gaps in security.

Sens. Jeff Flake (R-Ariz.) and Dianne Feinstein (D-Calif.) said this week they will introduce legislation that would tighten the program by ending visa waivers for people who have traveled to Syria and Iraq in the last five years.

Lobbyists for the travel industry group are rushing to meet with legislators to defend the program, which they say has adequate security and screening requirements. They are especially concerned about a proposal announced Monday by Sen. Rand Paul (R-Ky.), under which there would be a 30-day waiting period for people traveling as part of the program. Paul has yet to introduce the bill and his office said it is still being drafted.

Paul’s proposal would undermine the purpose of the program, which is to make travel more efficient for citizens of allied countries and to allow those countries to share intelligence information, said Jonathan Grella, executive vice president of public affairs for the U.S. Travel Association.

The visa waiver program, or VWP, was established in 1986 and facilitates the travel of about 20 million people to the United States each year. Participating countries include France, Belgium and the United Kingdom. Under the program, many business travelers, for example, make short trips to attend conferences and training sessions, or to negotiate contracts.

The travel association is critical of the visa provision of Paul’s draft bill but not the entire proposal, which also would suspend the issuance of visas to refugees from up to 30 countries, including Syria, pending strict background checks.

“We will be redoubling our efforts to educate lawmakers about VWP and its benefits,” Grella said. “We have made contact with various offices that are talking about doing something. We’re making plans on who’s going to quarterback various outreach.”

Members of the congressional intelligence committees have also questioned whether the visa program could be an easier path into the country for terrorists than the refugee resettlement efforts.

“Were I in Europe already, and I wanted to go the United States, and were I not on a watch list or a no-fly list and I wanted to get there, the likelihood is I would use the visa waiver program before I would try to pawn myself off as a refugee,” said Sen. Richard Burr (R-N.C.), chairman of the Senate Select Committee on Intelligence.

McCaul said Wednesday that the House could soon move legislation concerning the visa program.

“Obviously it’s a vulnerability when you have 5,000 foreign fighters with Western passports,” McCaul said. “We need to tighten up those security gaps.”

Under the visa waiver program, in order to board a U.S.-bound plane, travelers must clear the Electronic System for Travel Authorization (ESTA) — the Customs and Border Protection’s automated web-based system that helps determine whether an individual’s travel to the United States will pose a security risk. This requirement was added after 9/11 to enhance the security of the visa waiver program.

If the electronic system flags the name of an individual traveler, they would not be eligible to travel under the visa waiver program and would have to apply for a visa, and thus be interviewed and fingerprinted by officials with the State Department’s Bureau of Consular Affairs. And if an individual’s name were to be flagged during a flight manifest check, which is separate from the electronic system and is done on all travelers including U.S. citizens, they can be denied boarding.

Countries that join the program must share law enforcement and security-related data with the United States and maintain high counter-terrorism, law enforcement, border control and document security standards, according to the State Department.

“It enables countries to share intelligence and have the ability to identify problems before they materialize, and work together to make travel safer,” Grella said. “The whole point of it is that these alliances make everyone stronger rather than every country having to solve the security problem alone.”

In recent years, there have been some efforts to expand the program, particularly from lawmakers representing popular tourist destinations. In March, Reps. Joe Heck (R-Nev.) and Mike Quigley (D-Ill.) introduced the Jobs Originated Through Launching Travel (JOLT) Act, aimed at expanding the program.

“Without security, there can be no travel,” Grella said. “There needs to be security, but at the same time we need to ensure that freedom prevails over fear and the decisions we make in the aftermath of these horrible attacks need to be effective and on point. They can’t be an emotional overreaction.”