The Department of Transportation issued new guidance when dealing with service animals flying with their owners.

In addition to clarifying what airlines can and cannot regulate, the instruction issued by the federal agency is still giving the all-clear to miniature horses flying in the cabin if they are a service animal.

Miniature horses are not a common service animal, but they can be, WJZ reported. They can live to be about 35 years old and are between two and three feet tall, weighing about 100 pounds when fully grown.

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The regulations are a guideline that airlines can follow. But they don't have to. If airline officials ignore the instructions they can be penalized, WJZ reported.

But not all service animals are protected under the same guidelines.

Airline officials can make a case-by-case determination when it comes to snakes, reptiles, ferrets, rodents and spiders, according to WJZ.

The Department of Transportation will also look at enforcement about other species that are emotional support animals on a case-by-case basis.

The guidelines released last week said airlines have asked the department to "categorically ban" some species like "birds, hedgehogs, insects and animals with hooves or horns." But the DOT said that the determination will be made through the rulemaking process that is revising the Department of Transpiration's Air Carrier Access Act.

Airlines now have about 30 days to revise policies that govern service animals, WJZ reported.