Since the 2016 U.S. presidential election nearly a year ago, there has been increasing scrutiny of how Russian-backed operatives used accounts on Facebook, Google and Twitter to try to influence its outcome.

Executives from those companies appear before at least three congressional hearings starting Tuesday, facing questions from lawmakers about what happened and how they plan to respond.

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For years, the internet was viewed as “an egalitarian force, basically giving voice to the voiceless,” said Nate Persily, a Stanford University law professor.

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“We realized that once you allow anyone to speak to as many people as they want no matter when they want, that enables certain types of speakers who hold undemocratic speech,” Persily said.