The government is telling airlines and passengers how it will enforce rules governing animals that people bring on planes.

The Transportation Department said Thursday that airline employees can bar any animal they consider a safety threat. Airlines, however, can be punished if they ban an entire dog or cat breed, such as pit bulls.

The department’s enforcement office says it doesn’t plan to stop airlines from asking passengers “reasonable” questions about a service animal’s vaccinations, training and behavior. Airlines can require advance notice if passengers have an emotional support animal.

The number of animals on planes has been rising in recent years as more people bring a companion for emotional support. Most flying pets are tame, but there have been some well-publicized instances of animals biting passengers or airline employees.