A contingent of Senate Democratic Conference members want Facebook to voluntarily disclose more about the sources of advertising dollars on the social media platform.

The group led by New Jersey’s Robert Menendez, highlights in a letter to Facebook CEO Mark Zuckerberg efforts by Russia to use Facebook to spread political messaging to undermine the U.S. electoral process.

“More than a year ago, after news reports revealed that Russian agents used Facebook to spread inflammatory posts to over 126 million Facebook users, Facebook promised Congress that it would provide additional disclosures on political ads,” the letter read. “Yet, you continue to take in ad revenue from companies cloaked in secrecy. Although no legal requirement exists mandating that political advertisers on social media platforms file disclosures with the Federal Election Commission, you could take it upon yourself to mirror the laws that exist for radio and television ads.”

The senators cited reporting about a group that pushed a concealed carry permit certification program for gun owners, to the tune of $2.5 million.

Joining Menendez were Sens. Richard Blumenthal of Connecticut, Sheldon Whitehouse of Rhode Island, Kirsten Gillibrand of New York, Edward J. Markey of Massachusetts, Tom Udall of New Mexico, Sherrod Brown of Ohio, Mazie K. Hirono of Hawaii and Bernie Sanders of Vermont.

“We believe you also have a moral responsibility to ensure that your users are able to discern who and what is behind political ads shown on your platform. Such transparency will help ensure open and fair elections, free of dark money or foreign interference,” the senators wrote, stressing a loss in confidence of customers.

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