Pointing to misinformation campaigns spread by authoritarian regimes, U.S. Sen. Michael Bennet on Monday wrote to the CEO of Facebook, Mark Zuckerberg, asking what steps the company was taking worldwide to combat “coordinated inauthentic behavior” that influences elections.

“In the Philippines, Facebook staff trained [President] Rodrigo Duterte’s campaign, which then used the platform to circulate disinformation, including a fake endorsement from the pope and a fake sex tape of a political opponent,” Bennet said. “Although Facebook has since organized safety and digital literacy workshops while hiring more Tagalog speakers, journalists still contend that Facebook hasn’t ‘done anything to deal with the fundamental problem, which is they’re allowing lies to be treated the same way as truth and spreading it'”.

Bennet’s inquiry came in response to an op-ed from Zuckerberg published on Feb. 16 in The Financial Times. Zuckerberg argued that social media platforms that accumulate users’ data should not have the sole responsibility for determining how to balance privacy with free expression. He called for world governments to pass regulations to give companies like Facebook clear guidelines for security practices.

“Rather than relying on individual companies to set their own standards, we’d benefit from a more democratic process,” he wrote. “This is why we’re pushing for new legislation, and it’s why we support existing US proposals to prevent election interference.”

Bennet, pointing to Facebook’s nearly three billion users across platforms such as Messenger, WhatsApp and Instagram, labeled as inadequate Facebook’s efforts to prevent manipulation of public opinion over social media. Specifically, he cited Facebook’s lack of Burmese speakers to identify hate speech in Myanmar and Duterte’s use of “trolls” in the Philippines to spread misinformation about journalists and political opponents.

“What has Facebook learned from its efforts to limit coordinated inauthentic behavior in the Brazilian and European Union elections?” Bennet asked in the letter. He wanted to know how Facebook planned to limit the ability of hate speech and disinformation to become viral, asking for a response by April 1.