Several accounts [1] [2] [3] have noted that the Senate Intelligence Committee has requested information regarding related to President Donald Trump, his senior officials and his campaign staffers from the Treasury’s FinCEN. What is FinCEN?

It’s shortened form for “Financial Crimes Enforcement Network”.

From the official website:

The mission of the Financial Crimes Enforcement Network is to safeguard the financial system from illicit use and combat money laundering and promote national security through the collection, analysis, and dissemination of financial intelligence and strategic use of financial authorities.

For the record, the current acting director is Jamal El-Hindi (as of 2:22PM Pacific).