Regulators are allowing U.S. airlines to restrict the number of emotional support animals on flights. The Department of Transportation said it will not penalize airlines if they refuse to let passengers take aboard more than one support animal. Service animals like seeing-eye dogs will not be restricted under the proposed changes. The action came as the three largest U.S. carriers have altered their policies on animals since the start of this year. The increased numbers of animals have led to at least two incidents in which passengers were injured in flight. Airlines will now be allowed to request information that a passenger has a disability or require proof of an animal’s vaccination and training.