As per the guidelines, when any traveler takes a piece of additional luggage, United Airlines baggage fees will have to be submitted by him/her. Infants flying abroad (including destinations to Canada, Guam, and Mexico) who do not have a seat must buy a ticket and pay infant rates and taxes. When you wish to bring another pet with you, purchase an additional ticket under the United Airlines baggage policy. You can pay a higher $125 each way for carrying your pet.