An Airbus A321 from the Delta fleet. (Delta Air Lines file photo)

ATLANTA - Delta Air Lines has joined a growing number of air carriers who will no longer allow emotional support animals on flights.

Atlanta-based Delta announced that the new policy banning the animals will go into effect on January 11, 2021.

According to the airline, the U.S. Department of Transportation issued new guidance in December which made recognizing emotional support service animals a requirement.

"We applaud the DOT for making this change and acknowledging the concerns that Delta and many other stakeholders have raised for the past several years," said Allison Ausband – S.V.P., In-Flight Service. "The DOT’s final rule enables airlines to put the safety of all employees and customers first, while protecting the rights of customers who need to travel with trained service animals."

Trained service animals are defined as dogs regardless of breed, specifically trained to assist a person with a disability, Delta said.

However if a trained service animal appears to be a threat or behaves aggresively or inappropiately, it will not be allowed to board a Delta plane.

American Airlines and United Airlines have also announced that emotional support animals will no longer be allowed to fly. Alaska Airlines has done the same.

The number of passengers flying with companion animals grew rapidly in recent years, with some saying the animals helped them overcome anxiety and other issues. Passengers only needed a note from a health professional, and a cottage industry sprang up to provide those notes along with vests and other accoutrements for their animals.

Airlines and particularly flight attendants took a more critical view, saying passengers were exploiting a loophole in federal regulations to avoid pet fees. In a few cases, including some involving serious injuries, companion animals bit other passengers.