For several years, the Transportation Security Administration has surprised many passengers with free access to TSA Precheck, the agency’s expedited security lane, where travelers need not remove coats and belts, nor take toiletries or laptops from bags.

But for some passengers, that perk may soon disappear.

The TSA has informed airlines that starting in February it will “significantly reduce” the number of passengers randomly selected for faster screening. It doesn’t mean passengers will never receive expedited security without joining the program, but it suggests some travelers who rely on free access may not receive it so often.

“This is part of the natural progression of the TSA Precheck program,” an agency spokesman said in an email. “We intend to only have enrolled or pre-vetted passengers, or those screened by K9s, in the expedited screening lanes.”

TSA designed its expedited security program, called Precheck, for frequent travelers who pay an $85 fee and undergo a background check after giving their fingerprints. Members can also join by enrolling in the U.S. Customs and Border Protection’s Global Entry program. But while membership in TSA Precheck is growing — more than 12 million people have opted in — the agency remains far short of its goal of enrolling 25 million passengers by 2019.

With fewer passengers enrolled than expected, TSA sometimes gives expedited security to non-Precheck members. “Depending on the risk-based calculation, a passenger might have received expedited screening on a flight-by-flight basis,” the agency spokesman said.

That’s great news for passengers surprised by short security waits, but some experts have criticized the agency for its light screening on passengers who have not passed the background check.

This is not the first time TSA has said it will reduce the number of non-members receiving expedited security. In September 2015, TSA ended what it called its Managed Inclusion II program, in which behavior detection officers gave some travelers access to Precheck lanes. Agents would test those travelers for explosive residue.

One reason TSA started allowing non-Precheck passengers to use expedited security was to make regular security lines move faster, but the agency’s spokesman said this new policy should not affect queues.

“We do not anticipate that this will affect lines, because the mitigating measures we put in place last year are still in place,” the spokesman said. “That said, TSA will monitor the operational impacts of these changes on airport checkpoints and on TSA Precheck enrollment capabilities and adjust resources accordingly.”

An American Airlines spokesman said the carrier is recommending customers to join the program.

“The TSA has informed American Airlines that starting early next month, TSA will significantly reduce access to TSA Precheck expedited screening for passengers who do not have a Known Traveler Number,” the spokesman said. “American and the TSA strongly recommend that customers enroll in a DHS trusted traveler program in order to receive TSA Precheck when they fly American.”