CHICAGO >> United Airlines is joining other major U.S. carriers in no longer allowing emotional-support animals to fly for free.

United said Friday that starting Monday, it will no longer let passengers book travel for companion animals. For people who book before the deadline, free travel for companions will end Feb. 28.

After that, United said, only trained service dogs can fly in the cabin while not being in a carrier. Owners will have to submit a government-approved form attesting to the dog’s training, vaccines and disposition. Therapy animals trained to visit nursing homes and other settings don’t count as service dogs, United said.

Owners may be able to transport other animals in the cargo hold or in carriers that fit under a seat in the cabin. Either way, the owner will pay a pet fee, which starts at $125 per flight.

Alaska Airlines, American Airlines and Delta Air Lines announced similar policies in the last several days. The moves follow a Transportation Department rule that lets airlines crack down on the growing number of emotional-support animals in recent years.

The government rules announced last month require airlines to accept service dogs that are trained individually to help a person with a disability. The rules let airlines deny free boarding for companion animals.

For many years, thousands of passengers relied on a previous regulation to bring an animal on board for free by claiming that it provided emotional support. Airlines and flight attendants believed some passengers abused the rule to avoid pet fees.