United Airlines flight 422 from Houston to Seattle was diverted to Dallas an hour after takeoff, according to data from Flightradar24, Business Insider reported.
A Reddit account said the ground crew members spent over two hours cleaning up the mess, which was the result of the dog defecating next to the first-class toilet.
The account said the smell did not completely go away, and the time spent resolving the incident also meant that the food on the plane went bad.
Business Insider said United Airlines confirmed the incident with the paper. The exact number of passengers on the plane at the time has not been confirmed.
Previously in February, a dog also relieved itself on a United Airlines plane and crew members cleaned up the mess. There was no need for an emergency landing at the time.