U.S. Treasury Department's financial crimes unit Wednesday proposed a plan to require real estate professionals to flag suspicious activity, in a bid to curb illicit funds flowing through residential real estate.

The plan, proposed by Treasury Department's Financial Crimes Enforcement Network, would require reporting from real estate professionals involved in cash transactions for residential real estate.

Certain people involved in real estate closing would have to file and keep records of suspicious activity, according to FinCEN's proposal filed with the U.S. Federal Register.