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A group of House and Senate Democrats are calling on the U.S. government to issue new “guidance” to stop foreign advertisers from spending money on Facebook, Google and other web platforms in a bid to influence American elections.

Federal law already bars that sort of political spending, but lawmakers — including Rep. John Sarbanes and Sen. Elizabeth Warren — stress in a letter to the Federal Elections Commission that countries like Russia “have routinely deployed sophisticated tactics in making political expenditures to evade detection.”

To that end, the Democrats are asking the FEC — which oversees campaign finance —to offer suggestions for how to crack down on “loopholes” that allow foreign entities to use “corporate or nonprofit designations to evade disclosure.” And they want to help tech companies harden their own platforms to prevent that spending in the first place.

For now, though, the Democrats are asking the watchdog agency to issue a timeline for action and respond to their questions no later than Oct. 4.

“I have confidence the Googles and Facebooks and Twitters of the world have the capacity — they certainly have the resources — to put systems in place that can get behind these issues,” said Sarbanes, who spearheaded the missive, in an interview with Recode. “[We want to] figure out: Where is the money coming from? Who’s responsible for it?”

Other signees include Sens. Cory Booker of New Jersey and Kamala Harris of California.

The letter comes weeks after Facebook admitted that Russian propagandists spent more than $100,000 on Facebook ads in an effort to influence the 2016 presidential race. For that reason, the social giant has found itself drawn into the U.S. government’s official investigation into allegations of Russian meddling in the election, a probe led by former FBI Director Robert Mueller. So, too, has Facebook drawn special scrutiny from Congress, where some House and Senate lawmakers now want the company to testify about the reports in open hearings.

In the meantime, Democrats have called for stronger, tighter political advertising disclosure laws at the FEC, though previous attempts to regulate campaign finance law have been met with sharp resistance from Republicans at the agency.

Others, like Sarbanes, are exploring the need for legislation, but that too might face an uphill battle on an especially partisan Capitol Hill. Perhaps tellingly, Sarbanes and his allies didn’t obtain even one signature on their letter from a Republican lawmaker.

“Unfortunately, I think that there’s been sort of an edict from on high within the leadership of the Republican party that anything that involves Russia in any way, if the word even appears, somehow that then creates this entanglement with the broader Russian investigations,” Sarbanes said. “They don’t want to touch that and so they prefer their members stay away.”

But Sarbanes hopes that will change — and soon — with the 2018 congressional elections fast approaching. “We have time to get it done but that window will close very quickly,” he said.

Here’s the full letter.

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