Twitter is rushing to reassure advertisers that it will remain a safe place for brands after Elon Musk takes over the company, as the campaign groups that organised a Facebook advertising boycott in 2020 warn that the Tesla chief’s focus on freedom of speech could increase toxicity and abuse.

The San Francisco-based company has written to agencies in the wake of Monday’s $44bn deal announcement, insisting the company remains committed to ensuring their ads are not placed alongside harmful or offensive content, according to an email seen by the Financial Times.

That outreach reflects concern that Musk’s stated position as a “free speech absolutist” could hurt Twitter’s $4.5bn-a-year advertising business built around the social media platform being attractive to traditional marketers.

The company’s pledge of “brand safety” has been challenged by Jonathan Greenblatt, chief executive of the Anti-Defamation League, which led 2020’s Stop Hate for Profit campaign against Facebook, when dozens of brands including Unilever, Ford and Coca-Cola pulled spending from the social network.

“Twitter has made some strides in tackling online hate and extremism in recent years, and so while we want to be cautiously optimistic about how Elon Musk will run the platform, he has not demonstrated any focus on these issues to date,” Greenblatt said. “We worry that he could take things in a very different direction.”

Other campaign groups, including the National Association for the Advancement of Colored People and Color of Change, have voiced similar concerns, while Brussels has also warned Musk that Twitter must comply with new EU rules on content moderation.

Twitter declined to comment.

The initial response of advertisers to the change in ownership has been mixed. Some have welcomed Musk’s plans to authenticate users and squash fake accounts or “bots”, while others fear he will undo the progress Twitter has only recently begun to make in improving its content moderation.

“In general, the expectation is that Musk’s comments will lead Twitter towards becoming more toxic and less brand-friendly,” said Brian Wieser, global president of business intelligence at media agency GroupM. Actively reversing its policing of abuse is “not something that would be well received” by brands, Wieser added.

“Advertisers are planning for the possibility that they will need to shift spend,” said an executive at one large agency.

Most advertisers are willing to wait and see, rather than pull their budgets immediately. “A reduction in fake accounts would be positive,” said Mark Read, chief executive of marketing group WPP. “We have to see what impact Elon Musk has on Twitter’s moderation policies and content.”

However, brands and executives in one particular industry have already begun to raise the alarm: automotive companies.

Some carmakers are worried that their marketing campaign plans will leak to Tesla, according to one agency executive, while they are also reluctant to spend money on a platform that is now closely associated with one of their biggest rivals.

Henrik Fisker, chief executive of electric vehicle maker Fisker, deleted his Twitter account soon after the deal was announced, telling people to follow him on Instagram instead.

General Motors said: “We will review the standards and approach of Twitter as it evolves under its new ownership structure and determine the best course of action for our company and consumers.”

Stephan Loerke, chief executive of the World Federation of Advertisers, a trade body, said: “Where you put your ads and the content next to them on the platform has an impact on the reputation of the company.

“We hope that the new [Twitter] leadership embraces the need for balanced moderation on top of these necessary controls [for users and advertisers].”

Additional reporting by Steff Chávez, Patricia Nilsson and Peter Campbell