By Blake Brittain

Billionaire Elon Musk's decision to rebrand Twitter as X could be complicated legally: companies including Meta and Microsoft already have intellectual property rights to the same letter.

X is so widely used and cited in trademarks that it is a candidate for legal challenges - and the company formerly known as Twitter could face its own issues defending its X brand in the future.

"There's a 100% chance that Twitter is going to get sued over this by somebody," said trademark attorney Josh Gerben, who said he counted nearly 900 active U.S. trademark registrations that already cover the letter X in a wide range of industries.

Musk renamed social media network Twitter as X on Monday and unveiled a new logo for the social media platform, a stylized black-and-white version of the letter.

Owners of trademarks - which protect things like brand names, logos and slogans that identify sources of goods - can claim infringement if other branding would cause consumer confusion. Remedies range from monetary damages to blocking use.

Microsoft since 2003 has owned an X trademark related to communications about its Xbox video-game system. Meta Platforms - whose Threads platform is a new Twitter rival - owns a federal trademark registered in 2019 covering a blue-and-white letter "X" for fields including software and social media.

Meta and Microsoft likely would not sue unless they feel threatened that Twitter's X encroaches on brand equity they built in the letter, Gerben said.

The three companies did not respond to requests for comment.

Meta itself drew intellectual property challenges when it changed its name from Facebook. It faces trademark lawsuits filed last year by investment firm Metacapital and virtual-reality company MetaX, and settled another over its new infinity-symbol logo.

And if Musk succeeds in changing the name, others still could claim 'X' for themselves.

"Given the difficulty in protecting a single letter, especially one as popular commercially as 'X', Twitter's protection is likely to be confined to very similar graphics to their X logo," said Douglas Masters, a trademark attorney at law firm Loeb & Loeb.

"The logo does not have much distinctive about it, so the protection will be very narrow."

Insider reported earlier that Meta had an X trademark, and lawyer Ed Timberlake tweeted that Microsoft had one as well.

(Reporting by Blake Brittain in Washington; Additional reporting by Sheila Dang; Editing by Peter Henderson and Sonali Paul)