A member of the Congressional Black Caucus is pushing Facebook to strengthen its advertising standards after Russian operatives used the company’s ad service to attack groups like Black Lives Matter during the 2016 election s.

In a letter sent to Facebook CEO Mark Zuckerberg on Tuesday, Rep. Robin Kelly pressed the company to “ensure that discriminatory and tactically divisive ad-targeting is aggressively prevented.”

The Illinois Democrat pointed to Russian-linked Facebook pages that promoted “incendiary anti-immigrant rallies, targeted the Black Lives Matter movement and focused attentions on critical election swing states like Wisconsin and Michigan.” Her letter was obtained by The Hill and first reported by The New York Times.

“It is my belief that Facebook cannot be the Trojan horse through which America’s vulnerabilities are exploited,” Kelly continued.
Facebook confirmed its receipt of Kelly’s letter and said that the company has been speaking with her office.

The social media behemoth is coming under intense scrutiny, with lawmakers seeking more information about how Russia may have used Facebook to sow discord in the U.S. and influence the 2016 elections.

The company had initially denied that Russia had used its platform. That changed on Sept. 6, when Facebook said that it discovered that a Kremlin-linked group purchased $100,000 in political advertisements in advance of the 2016 elections.

Subsequent reports revealed that many of the ads were aimed at exploiting social and racial divisions. One prompted Facebook users to attend an anti-Muslim, anti-immigration rally in Idaho. Others were aimed at branding Black Lives Matter as a political threat.

Facebook said last week that it will turn over all 3,000 of the ads purchased by the Russian group to congressional Investigators.

Lawmakers like the Senate and House Intelligence committees’ top Democrats, Sen. Mark Warner (Va.) and Rep. Adam Schiff (Calif.), respectively, say this a good first step but would like to see more from the company.

Their committees will hold public hearings on the matter and have invited Facebook, along with Twitter and Google, to attend.

None of the companies have offered comment on if they will appear at the hearings. Warner said on Thursday that he is considering subpoenaing company representatives to appear.