As regulators threaten to clamp down on ride-sharing companies illegally operating at airports, Uber has tweaked its algorithm at Los Angeles International Airport so that drivers’ phones will not receive ride requests if they are near the terminals.

The “geofence” is designed to keep Uber drivers from clogging the roads and parking structures as they clamor for customers.

In other parts of the city, when a passenger requests a car, the fare goes to the driver that is closest. Now, Uber’s algorithm will allow drivers to accept LAX ride requests only if they are within a triangular swath of the limousine parking lot at Westchester Parkway and Jenny Avenue.

The geofence has raised hackles amongst drivers because the new system doesn’t take into account how long someone has been waiting for a new fare. For example, a driver who arrives at the airport at 7 a.m. will not necessarily receive a ride request before someone who shows up at 10. Drivers say the algorithm is random.

“They need a first-come, first-serve system,” Uber driver Narek Gasparyan said as he stood in the shade of a tree with two dozen other drivers last week. “I just got here and I might get a call and leave right away. That’s not fair to the other guys.”

The geofence at LAX is the latest curve ball Uber has thrown at professional drivers in Southern California, who have struggled to stay afloat as Uber and other app-based car-sharing services like Lyft and Sidecar continue to disrupt the for-hire car industry.

Uber’s luxury car services — called UberBLACK and UberSUV — employ commercially licensed and insured drivers. The company’s more economical UberX line is called a transportation network company, or TNC. These companies, which include Lyft and Sidecar, allow just about anyone with a car to sign up as a driver.

TNCs have come under attack from taxi companies — who want TNC drivers to be held to the same regulatory standards as cabbies and professional chauffeurs — and from groups concerned with public safety.

The taxicab administrator for the Los Angeles Department of Transportation issued cease-and-desist letters to Sidecar, Lyft and Uber last summer. Then the California Public Utilities Commission voted in September to allow TNCs to do business in the state, with the caveat that they obtain special permission before operating at airports.

None of the TNCs have received airport permits yet, but LAX is in the process of drafting license agreements that would allow TNC drivers without commercial licenses to pick up passengers there.

One of the sticking points is ensuring that drivers are commercially insured. Legislation is working its way through the state Senate that would force TNCs to improve insurance coverage for its drivers.

The issue made headlines after an Uber driver struck and killed a 6-year-old girl in San Francisco on New Year’s Eve. Uber claims the driver was not working for the company because there was no passenger in the car at the time of the collision, although the app was turned on. The family of the girl is suing Uber and the driver.

The geofence at LAX was an idea advanced by Los Angeles World Airports, the agency that runs LAX, as a way to manage the numbers of vehicles that come into the terminal and parking structures, airport manager Selena Birk said.

LAX police have impounded 40 ride-sharing vehicles for attempting to pick up fares at the curb, a LAWA spokesperson said. Most of those have occurred within the past two weeks.

Uber’s geofence is probably an attempt to placate the CPUC, which issued a strongly worded letter to TNCs in June that admonished the companies for not complying with airport regulations. The commission is scheduled to vote on new TNC regulations on Thursday. Uber is expected to address the panel during public comments.

Uber refused to discuss the geofence. “We are constantly working to maximize driver partners’ opportunities to connect with riders while also coordinating with airport traffic flow,” spokeswoman Eva Behrend said in an email.

Sidecar said it does not currently use geofence but is considering it. Lyft did not immediately respond to questions related to geofencing.

The UberBLACK and UberSUV drivers at LAX said they were frustrated with the company’s hands-off approach. Drivers can only communicate with their employer via email. Several drivers working Wednesday said they heard about the geofence from other drivers, not from Uber.

The drivers said they originally loved Uber because it helped them get more clients. They used to get ride requests every 15 to 30 minutes. Now, with so many new drivers flooding the market, it takes one to two hours to get a fare, and sometimes much longer.

Still unsure how the new algorithm works, the LAX drivers congregate at the end of the parking lot closest to the terminal, just in case proximity to the passenger is still a factor. The drivers place their phones on a makeshift table next to a light pole that straddles the geofence line.

One driver said some people believe the pole boosts their cellphone signals. Another driver said that was silly.

“When you’re staring at your phone three or four hours at a time, your arm gets tired.”