@United
United Airlines does not accept pets in the cabin. For each one-way flight, your pet must accompany you in the cabin. United will also charge $125 for each one-way domestic or international itinerary that has more than four hours stopovers. United has a limit on the number of pets it will allow in-cabin for certain flights.
United allows you to add your pet to your booking at any time, but it is best to confirm that your pet is available when you book your flight. United does not charge change fees. However, you will have to reschedule your trip if the flight doesn't allow more animals in-cabin.