An Audi spokesperson said the German auto maker was pausing ads and "will continue to evaluate the situation", while a spokesperson for General Mills, the US company behind food brands such as Cheerios, said it would "continue to monitor the new direction and evaluate our marketing spend".
Advertisers are concerned about whether content moderation will remain as stringent under Musk - a self-described "free speech absolutist" - as it has been, and whether staying on Twitter might tarnish their brands.
Shortly before taking over the San Francisco company last week, Musk vowed to advertisers that he would not allow Twitter to become a "free-for-all hellscape", an indication there would still be consequences for violators of its rules against harassment, violence or election and COVID-related misinformation.
But since then some users have posted racial slurs and recirculated long-debunked conspiracy theories in an apparent attempt to see if the site's policies were still being enforced.
Civil rights group the NAACP this week expressed to Musk its concerns about the "life-threatening hate and conspiracies" that have proliferated on Twitter under his watch.
Last week, General Motors announced a pause on Twitter advertising while it worked to "understand the direction of the platform".
Ad giant IPG Mediabrands sent a recommendation to clients on Monday that they pause advertising on Twitter for a week until more clarity emerged about brand safety on the site.
Some advertisers could evaluate their plans after Twitter's new "content moderation council" meets. Musk has said he will not reinstate any accounts or make major content decisions before it is convened. No date has been announced for that meeting.
About 90 per cent of Twitter's revenue comes from advertisers but it's far from the biggest platform for digital marketing, with Google, Amazon and Meta accounting for about 75 per cent of advertising.
Twitter has lost most of its top executives in the past week, including the one in charge of advertising sales.
Chief customer officer Sarah Personette resigned on Friday, but said she still believed Twitter's new administration understood the importance of upholding "brand safety" standards.
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