In a letter sent to brands Tuesday ahead of the 2022 NewFronts digital advertising conference, more than two dozen civil society groups said marketers should secure commitments from Twitter to retain its most critical policies, including on civic integrity and hateful conduct, and threaten to withdraw funding if Twitter does not comply.

"As top advertisers on Twitter (TWTR), your brand risks association with a platform amplifying hate, extremism, health misinformation, and conspiracy theorists," the letter said, adding: "Your ad dollars can either fund Musk's vanity project or hold him to account."

Twitter didn't immediately respond to a request for comment. In an investor filing Monday, Twitter told advertisers "we have no planned changes to our commitment to brand safety" but that the company "cannot speculate on changes Elon Musk may make post closing."

The letter, first reported by CNN, urges advertisers to make their next ad deals with Twitter contingent on changes to platform policy under Musk.

It offers the latest example of how some advocacy groups have leaned on the immense power of corporate speech — and specifically digital advertising, the lifeblood of many tech platforms — in attempts to shape tech companies' behavior. It leverages years of growing realizations by the ad industry that brands can face reputational damage if their ads appear next to white supremacist content or other harmful material.

Tuesday's initiative bears echoes of a far-reaching advertising boycott in 2020 that saw companies ranging from Adidas to Starbucks pulling their ads from Facebook over what they said were its failures to keep hate speech from spreading. But unlike that campaign, the groups behind Tuesday's letter said advertisers have a chance to be more proactive and strategic this time, because Musk has already telegraphed what he plans to do with Twitter. (The Tesla CEO and SpaceX founder has pledged to restore "free speech" to the platform by, among other things, easing up on content removals and account bans. He also wants to "authenticate all real humans" on Twitter.)

As advertisers prepare to negotiate forward-looking contracts with Twitter this week during the NewFronts conference, they can preemptively protect themselves from any damage to their brands resulting from Musk's eventual takeover, said Angelo Carusone, CEO of Media Matters for America, one of the organizations behind the letter.

"If Elon Musk comes in and gets rid of all the brand safety protections, I think Coca-Cola should be able to cancel their contract," Carusone said. "It would be very revealing if Twitter refuses to or does not sign or does not give those cancellation options."

Tuesday's letter targeted other big-name advertisers, as well, including Apple, Best Buy and HBO — the last of which is owned by WarnerMedia, CNN's parent. Spokespeople for the brands didn't immediately respond to requests for comment.

Other organizations spearheading the letter campaign include the technology advocacy organization Accountable Tech and the feminist group UltraViolet. Meanwhile, the Center for Countering Digital Hate, the National Hispanic Media Coalition and the digital rights group Free Press also signed the letter in support of the effort.

In addition to contract terms that would commit Twitter to enforcing its existing policies, the letter said brands should require Twitter — as part of any ad deal — not to restore the accounts of individuals who have already been banned from the platform, such as former President Donald Trump.

Advertisers should also require Twitter to continue to support academic research based on the company's data and implement protections to make sure spammers and other "bad actors" cannot benefit from Musk's proposal to "open-source" Twitter's algorithm, the letter said.

As Musk prepares to take control of one of the world's most influential tech platforms, Tuesday's letter from civil society groups could find a receptive audience. Last week, according to the Financial Times, Twitter wrote a message to advertisers addressing perceived nervousness about the Musk deal — and reassuring brands that Twitter will continue to be a safe place to advertise.

Even if Musk ultimately decides against undoing Twitter's policies, his sole ownership of the company highlights his unaccountable power, said Nicole Gill, co-founder and executive director of Accountable Tech. Gill added that because Musk has sought to pay for Twitter with loans against Tesla and Twitter shares, he could be more vulnerable to downturns in Twitter's business than he may let on. ("I don't care about the economics at all," Musk has said of Twitter's business.)

"The way this deal is structured, he has to care," Gill said.