ATLANTA — Delta Air Lines says it's no longer allowing passengers to fly with "pit bull type" dogs as service or support animals, a policy that's being met with criticism by groups that train service dogs and the people who use them.

The Atlanta-based airline describes its ban as an "enhancement" to its policy on animals in passenger areas. Delta will also limit travelers to a single emotional support animal per flight. The changes, announced this week, take effect July 10.

"It's a bit nuts because Delta is actually my preferred airline to fly with my service dog," said Fiona Gilbert of the San Francisco area, who said she flew about 300,000 miles with Delta in the past year with her pit bull-type dog, Koda.

Gilbert has a degenerative neurological condition, and Koda can sense when she might have a seizure and then get help if needed, she said.

"He's basically my alert system," she said. "He's my emergency response system. I trust him more than I trust myself when it comes to not feeling well. He's been trained to get help if I need him to. Koda and I are a team - we're inseparable."

Now, Gilbert has 20 trips planned with Delta later this year and is scrambling to figure out what to do.

Delta said its ban on pit bull-type dogs responds to "growing safety concerns" after several employees were bitten, the airline said in a statement.

"We must err on the side of safety," Delta said in a statement Friday. "Most recently, two Delta employees were bit by a pit bull traveling as a support animal last week. We struggled with the decision to expand the ban to service animals, knowing that some customers have legitimate needs, but we have determined that untrained, pit bull-type dogs posing as both service and support animals are a potential safety risk."

The bite happened during the boarding process for Delta flight 295 from Atlanta to Narita, Japan, the airline said.

But the ban is prompting a social media backlash, and is being criticized by several animal groups.

Delta "should resist unwarranted breed prejudice and rescind its breed ban," Matt Bershadker, president and CEO of the American Society for the Prevention of Cruelty to Animals, said in a statement Thursday.

Figuring out exactly which dogs fall under the policy could be a challenge.

"Pit bull is an arbitrary label - there's no standard definition of what makes a dog a pit bull," said Regina Lizik, the communications and fundraising manager at Animal Farm Foundation in Bangall, New York, which provides service dogs to people with various disabilities. Gilbert's pit bull was trained there.

"It's all about that individual dog and their ability to do this work," Lizik said. "All dogs are individuals."

Delta's statement says "pit bull type" dogs will be banned, but lists "Bull type dogs" on its online list of prohibited animals, which includes reptiles, spiders and goats, among others.

Gilbert said she understands Delta's desire to keep its employees safe. She said she supported the airline in March, when it announced new policies for service animals. Delta and United officials said at the time that they'd seen a sharp rise in the number of support animals, and that some passengers were bringing all types of animals on board.

"The irony is that I switched airlines to Delta when I got a service dog because they have the nicest flight attendants, and they are a wonderful company to fly with," Gilbert said.

Gilbert said she hasn't received complaints about Koda curled up by her feet on Delta flights in the past. Service dogs such as Koda are "much more polite and less disruptive than some passengers I've been on planes with," she said.

"Most people don't even know there's a 75-pound dog sitting there until we get up to leave," she added.