Facebook co-founder and CEO Mark Zuckerberg testifies before the Senate Judiciary and Senate Commerce Committees Tuesday to discuss the social media platform’s policy on user privacy amid the Cambridge Analytica scandal.

Cambridge Analytica is a political consulting firm that worked on then-candidate Donald Trump’s 2016 presidential campaign. The firm received a $15 million investment from Robert Mercer, a billionaire Republican donor, to influence voters, The New York Times reported.

The firm allegedly used a personality quiz to collect data and information from users and their friends, including details they had not intended to share. They are also accused of using private information from at least 50 million Facebook users’ profiles to influence elections. The committee will ask Zuckerberg about the scandal — the worst in Facebook’s history — and how the company failed to guard against other abuses of its service.