Elon Musk is demanding to know who was behind a letter signed by more than two dozen liberal groups that has urged advertisers to boycott Twitter if he completes his takeover of the social media giant.

Left-leaning NGOs — whose backers include billionaire financier George Soros and former Clinton operatives, as well as the European Union and the Canadian government — are urging a boycott of Twitter if Musk takes over the company.

“Who funds these organizations that want to control your access to information? Let’s investigate …,” Musk tweeted on Tuesday.

He added that “Sunlight is the best disinfectant.”

The letter, which was signed by 26 organizations, claimed that “Elon Musk’s takeover of Twitter will further toxify our information ecosystem and be a direct threat to public safety, especially among those already most vulnerable and marginalized.”

Musk taking control of Twitter means advertising on the platform “risks association with a platform amplifying hate, extremism, health misinformation, and conspiracy theorists,” the letter said.

“Under Musk’s management, Twitter risks becoming a cesspool of misinformation, with your brand attached, polluting our information ecosystem in a time where trust in institutions and news media is already at an all-time low,” the letter added.

“Your ad dollars can either fund Musk’s vanity project or hold him to account. We call on you to demand Musk uphold these basic standards of community trust and safety, and to pull your advertising spending from Twitter if they are not.”

The document’s letterhead includes the logos of three organizations — Accountable Tech, Media Matters for America, and UltraViolet.

Accountable Tech is a Washington, DC-based organization linked to top Democrats. Jesse Lehrich, a co-founder, once served as a spokesperson for Hillary Clinton’s presidential campaign. He is also the nephew of former Obama adviser David Axelrod.

Media Matters for America is an organization founded by political operative and Clinton backer David Brock. MMFA is a site “dedicated to comprehensively monitoring, analyzing, and correcting conservative misinformation in the U.S. media.”

UltraViolet is a feminist movement that is “mobilized to fight sexism and create a more inclusive world that accurately represents all women, from politics and government to media and pop culture.”

Other signatories, like Access Now, have the support of the Canadian and European governments as well as Soros, the billionaire financier who heads the Open Society Foundations.

Musk’s $44 billion takeover bid was accepted by Twitter’s board of directors last week. The world’s richest man has pledged to change the site’s content moderation policies in order to restore “free speech” to the platform.

Liberals fear Musk will allow Donald Trump, who was removed from Twitter after the Jan. 6, 2021, riots at the US Capitol, and other key conservative figures who were banned from the platform back onto the site.