A congressional committee investigating Russia’s interference in the 2016 presidential election has stepped up its probe over the past month, requesting that an agency that combats financial crime turn over confidential banking information on nearly 40 individuals and businesses, including at least nine who are American, BuzzFeed News has learned.

Senator Chuck Grassley, the chairman of the Senate Judiciary Committee, sent a letter to the Treasury Department’s Financial Crimes Enforcement Network — FinCEN for short — on September 29, seeking information about any suspicious financial transactions banks may have flagged on the individuals and businesses since Jan 2015. Banks are required by law to flag such transactions for FinCEN.

The Judiciary Committee is one of three congressional committees looking into Russian interference. Its investigation only recently got off the ground after months spent negotiating the scope of its probe, two staffers told BuzzFeed News, and a rift has reportedly been developing between Grassley and Dianne Feinstein, the top Democrat on the committee. Feinstein did not sign the letter to FinCEN. Asked why not and what she thinks of the request, she replied that Grassley "can send out a letter on his own. I mean, I don't have to sign any. So that's my answer."