Former President Obama warned Facebook founder Mark Zuckerberg to start taking the influence of fake news on his platform seriously ahead of President Trump’s inauguration, The Washington Post reported Sunday.

Obama reportedly pulled Zuckerberg aside at the Asia-Pacific Economic Cooperation summit in Peru in November and warned him that unless he cracked down on fake news, it would only get worse in the next election.

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Zuckerberg told Obama that fake news wasn’t a major issue on Facebook and that there was no simple way to address it, sources told The Post.

Facebook is now facing intense scrutiny over its role in the 2016 election, after the company revealed it had sold roughly 3,000 political ads to Russia-based groups during the course of the election.

Facebook handed the ads over to special counsel Robert Mueller and lawmakers are calling for representatives to testify before their committees about the ad sales.

Zuckerberg promised earlier this week that he and other executives at Facebook would be more transparent about ad sales as they try to minimize the site’s role in influencing elections.

“We will continue our investigation into what happened on Facebook in this election. We may find more, and if we do, we will continue to work with the government,” Zuckerberg said.