You have probably seen a dog in a emotional support animal vest at the airport this holiday season, but, is it legitimate?

California State Board of Guide Dogs for the Blind executive officer Brian Skewis told the Detroit Free Press that he has seen a "misuse" of the service dog law in airports. Service and emotional support animals travel for free.

The state's guide dogs agency issues licenses for guide dog training.

Sacramento International Airport spokesman Mark Haneke said that he is not aware of false service dogs being a problem at the airport, but anecdotally, he has seen a "tremendous rise" in emotional support animals.

"I’m sure some of these situations are legitimate, but sometimes it has appeared as a way to transport your pet for free (non-discrimination laws) – but again, a signed doctor’s letter is required, so someone officially signed off on the paperwork," Haneke said.

Air carriers such as American Airlines have acknowledged an increase in passengers traveling with emotional support animals.

But enforcement is not one-size-fits-all.

The U.S. Department of Transportation are considering rewriting the rules for service and emotional support animals.

Service animals are federally accepted and specific to trained dogs or miniature horses recognized by the Americans with Disabilities Act, while emotional support animals just provide emotional support.

RELATED: There's a legal difference between service and emotional support animals

Currently, there are guidelines for airline employees on the differences between a service animal and a emotional support animal. Requiring documentation for emotional support animals is to "ensure that passengers who have a legitimate need for emotional support animals are permitted to travel with their service animals on the aircraft."