When Trumpist Tom Fitton wondered on Twitter whether "@ElonMusk's @Twitter has tortious interference claims against the Left activist groups which are causing damaging advertiser boycotts of the platform?" Musk replied, "We do."
Wikipedia says tortious interference occurs "when one person intentionally damages someone else's contractual or business relationships with a third party, causing economic harm." The Wikipedia entry describes several examples of tortious interference, none of which include the word "boycott."
The activist groups that have asked Twitter to stop advertising on Twitter include the ADL and the NAACP. If Twitter files a lawsuit against either of these organizations it will go very badly for Musk.
Further, many global-brand advertisers dropped Twitter not because activists asked them to, but because they have seen Musk's out-of-control political trolling for themselves, like linking to the false story claiming Paul Pelosi wasn't attacked by a MAGA cultist but by a gay lover.
The fact that Musk is paying attention to what Fitton, a far-right troll who has filed lawsuits against climate scientists, has to say is all you need to know about Musk's promises to make Twitter "the most accurate source of information about the world." In June, Just Security released a study that revealed Fitton to the third most "repeat spreader" of false 2020 election claims among "far-right media entities and influencers, QAnon personalities, campaign advisors such as Rudy Giuliani, and the former president and his sons."