PHOENIX — The Phoenix-Mesa Gateway Airport is cracking down on Uber drivers by asking police to start citing them for trespassing.

Airport spokesman Ryan Smith says Uber drivers who pick up or drop off passengers are not operating legally because the ride-sharing service has not entered into a required formal agreement with the airport located southeast of Phoenix.

Ride-sharing services with an operating agreement have been allowed since late 2016. Uber’s competitor Lyft has been operating at the airport for nearly 10 months, paying a $2 fee per pickup and drop-off.

Uber spokeswoman Stephanie Sedlak tells the Arizona Republic that the company is negotiating with the airport.

Through formal agreements, Uber is operating at the Phoenix Sky Harbor International Airport and the Tucson International Airport.