New York (CNN) Facebook executives are facing mounting pressure, including from inside the company, to make sweeping changes to how the social media site runs political ads -- including reversing a controversial policy that allows politicians to run false ads and how voters are targeted on the platform.

On Monday night, the top Democrat on the Senate Intelligence Committee Sen. Mark Warner wrote to Facebook CEO Mark Zuckerberg and warned that Facebook's policies risked undermining American norms of "transparency, public deliberation and debate, openness, diversity of opinion, and accountability."

It's a further escalation of the debate over Facebook's responsibility for policing ad content, a week after Zuckerberg testified on Capitol Hill.

The Warner letter came just hours after The New York Times reported that more than 200 Facebook employees had signed a letter raising concerns about the company's political ad policy.

The concerns laid out by the employees and Warner go beyond the company's fact-checking policy and raise wider concerns about the power of Facebook's ad targeting.

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