Facebook will soon require political campaigns, advocacy groups and other entities that purchase ads about hot-button policy debates to disclose more information about themselves, as the social giant looks to prevent malicious actors from secretly spreading disinformation on its site.

The new rules governing “issue ads,” announced Friday, are aimed at Russia’s internet trolls and their ilk, which surreptitiously bought ads about contentious topics such as race, gun control and gay rights during the 2016 presidential campaign to try to stir social discord in the United States.

“These steps by themselves won’t stop all people trying to game the system,” Facebook chief executive Mark Zuckerberg wrote in a post Friday. “But they will make it a lot harder for anyone to do what the Russians did during the 2016 election and use fake accounts and pages to run ads.”

Zuckerberg also offered Facebook’s clearest support yet for pending federal legislation that would require the tech industry to disclose more information about political ads, including who buys them, and retain copies of them for public inspection. “Election interference is a problem that’s bigger than any one platform, and that’s why we support the Honest Ads Act,” Zuckerberg said. “This will help raise the bar for all political advertising online.”

Facebook’s announcements come days before Zuckerberg is due to testify to Congress on another matter – the company’s privacy practices and the controversy around Cambridge Analytica, a data analysis firm that improperly accessed as many as 87 million Facebook users’ personal data.

Yet political advertising could also come up at the hearings. One of the lawmakers set to grill Zuckerberg is Sen. Amy Klobuchar, D-Minn., a chief author of the Honest Ads Act.

“This is a positive step by Facebook to take the lead to put in place the transparency requirements called for in the Honest Ads Act, but a patchwork of voluntary measures from tech companies isn’t going to cut it – we need to pass the Honest Ads Act,” she said in a statement. “The goal of this legislation is to ensure that all major platforms that sell political advertisements are held to the same rules of the road.”

Facebook said it is still working out the details of its plan – including the exact definition of an “issues ad.” In a blog post, company executives said they’re consulting third parties to determine the specific topics that would trigger its new disclosure rules, which Facebook said would evolve over time.

Facebook will then require entities that seek to purchase issues-based ads to first verify who they are and their location offline – similar to Facebook’s announcement in October that those who buy ads that explicitly mention the names of political candidates would need to provide verification.

Beginning this spring – a few months before the 2018 congressional midterm elections – those ads about candidates and issues will feature an icon marking them as political. Facebook also said that it will offer a searchable index of the ads, including information about the users whom they targeted.