Twitter is considering legal action against Meta over its fast-growing rival app Threads.
Threads, which was launched to millions on Wednesday, is similar to Twitter and has been pitched by Meta bosses as a "friendly" alternative.
Twitter's Elon Musk said "competition is fine, cheating is not" - but Meta denied claims in a legal letter that ex-Twitter staff helped create Threads.
More than 30 million people have signed up for the new app, according to Meta.