The 30-year-old California-based rapper arrived in Burbank from a layover in Denver on Friday night to find someone else's pooch, the CNN reported.
"You guys r idiots... HOW U PUT MY DOG ON THE WRONG FLIGHT???? I need answers", he tweeted.
"My little dog been moving around since the AM, prolly has pee and number 2 all in his cage smh," the rapper said in a text message to CNN.
"....I plan on suing," he added.
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United Airlines says the dog is being well cared for.
"We're working as quickly as possible to reunite the pet with their owner later this evening. We have reached out to our customer and sincerely apologise for this mistake and are providing a refund. Pets are part of our customers' family, and their safety and wellbeing is of the upmost importance to us," the airline said in a statement.
In April, the airline came under fire for video of flight attendants and airport police violently dragging a man off an overbooked flight. A month later, a large rabbit - about to set a world record for side - died during a flight from the UK.