NEW YORK -- United Airlines is tightening its policy on emotional support animals on its flights.
Starting Monday, support animals are no longer allowed on flights longer than eight hours.
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United says it's making the change because of a rise in on-board animal-related incidents.
In addition, the Chicago-based airline will no longer allow kittens or puppies less than four months as support animals, in-cabin pets or service animals, saying animals that young typically haven't had all the necessary vaccinations.
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Delta and Spirit also recently changed their policies, now requiring at least 48 hours notice to bring service animals on flights.