Should emotional support animals be allowed on planes?

Millions are flying this holiday season and some people are bringing more than just carry-on luggage. Emotional support animals can help ease the stress of air travel. But with an increasing number of exotic animals on board, industry experts are calling for change.

After a stroke a few years ago, Valerie Pullman became nervous about flying. So, she takes Jonah the dog with her to keep her calm.

"If I'm feeling very anxious and he's there and I can pet him and be with him, it's like meditation for me," Pullman said.

Last year, more than a million passengers traveled with a variety of service and emotional support animals. But it's not just dogs and cats, people have brought on pigs, turkeys and even a miniature horse.

Passengers must present medical documentation for why the animal is necessary and they are supposed to be well-behaved. But Taylor Garland, a spokesperson for the Association of Flight Attendants, says that's not always the case.

"We need more concrete guidelines for emotional support animals because they are causing safety, health and security issues onboard our aircraft," Garland said.

Last year, Delta Airlines reported more than 40 instances of aggressive animal behavior in its aircraft cabins.

"We've had flight attendants go to the hospital, require stitches, or passengers having to be taken off on a gurney because of attacks from untrained emotional support animals," Garland said.

Now, certain airlines such as American and Delta are starting to limit emotional support animals to dogs and cats. But industry experts say that doesn't go far enough and the federal government needs to get involved.

"It's like throwing gasoline on a fire. Everything is just getting worse right now," said Charlie Leocha, the president of the consumer group Travelers United.

Leocha says there are no current limits on the number of support animals per aircraft, but the Department of Transportation is expected to release new rule proposals before the end of the year.

"They'll be trying to come up with a system for everybody, whether they'll be able to do it, I don't know," Leocha said.

Until a system is in place, the rules will remain up in the air.