It's been well documented that pets can make us mentally and physically healthy: Petting them can cause relaxation and even help lower blood pressure, and they can motivate us to stay active.

Some rely on their pets for emotional support, but there are some airline customers who may be stretching the "truth of need" a bit to travel with their pets.

Now Delta Airlines is cracking down and other airlines may soon follow.

We're not talking about service dogs that are trained for months to help owners deal with medical conditions. Those pets are trained to stay calm in a variety of settings and are allowed to go practically anywhere.

They know how to behave, but many pet passengers do not: Delta reports an 84 percent spike in animal incidents, including urination, defecation, and biting.

While many consider their pets a necessity, flying with Fido can cost up to $600. However, Fido's free if he's an emotional support animal.

Experts say more and more people are cheating the system and getting their pets ESA certified over the internet without any training, and that's why Delta will implement new rules Mar. 1 to make it more difficult to pass of Petunia as a support pet.

Under the new rules, you must provide the pet's ESA certification, proof of health, and a signed document saying your pet has been trained. You must sent the documents to Delta at least 48 hours ahead of your flight.

Owners of service and emotional support animals will also need to sign a statement vouching that their animal can behave.

The point of this is to reduce fraud: Delta carries about 700 service or support animals daily (about 250,000 a year). Last June one passenger's emotional support dog attacked another passenger and put him in the hospital.

It can be a serious issue, and it's not surprising that other airlines may follow suit.