Last week, right-wing circles were buzzing over a secret memo written by Rep. Devin Nunes (R-CA), ostensibly detailing corruption in FBI surveillance practices. It’s unclear how much is in the memo itself — even the FBI hasn’t seen it — but it didn’t stop skeptics from rallying behind the cause, launching #releasethememo into trending topics on both Twitter and Facebook.

Now, that campaign has come under investigation for Russian interference. In a letter to Mark Zuckerberg and Jack Dorsey, Rep. Adam Schiff (D-CA) and Sen. Dianne Feinstein (D-CA) called for Twitter and Facebook to conduct an investigation into whether Russian troll accounts had fueled the rise of the hashtag as part of a broader campaign. The Alliance for Securing Democracy had reported significant Russian activity on the hashtag, although the methods behind that attribution remain unclear.

“If these reports are accurate,” the letter reads, “we are witnessing an ongoing attack by the Russian government through Kremlin-linked social media actors directly acting to intervene and influence our democratic process.”

Schiff and Feinstein ask the companies to detail how many accounts linked to Russian influence operations were involved in the hashtag, and how many legitimate users have been exposed. The resulting report is to be presented to Congress and the public by January 26th — a deadline of only three days.

“Twitter is committed to addressing malicious activity on our platform, and we take any assertions of such activity very seriously,” a spokesperson said when reached by The Verge. “We look forward to working closely with Senator Feinstein and Congressman Schiff to address their questions.” Facebook did not immediately respond to a request for comment.

Both companies have already come under significant fire for running Russia-funded election ads during the campaign, a violation of federal election law. Last year, Facebook and Twitter testified before Congress and compiled detailed reports on Russian ads. The problem of unpaid troll accounts has proven even harder to address, and there are few proposals from either Congress or the industry on how to address the problem. Earlier this month, Twitter admitted that as many as 700,000 users had been exposed to Russian propaganda over the course of the campaign.

Update 12:11PM ET: Updated with comment from Twitter.