The U.S. Treasury Department's financial crimes unit proposed a long-awaited draft rule Wednesday aimed at stemming the tide of illegal cash funneled through real estate.

The Financial Crimes Enforcement Network's plan, to be published Feb. 16, would require real estate professionals involved in all-cash residential real estate transactions to flag suspicious activity. Treasury Secretary Janet Yellen last year estimated that criminals laundered $2.3B through U.S. real estate between 2015 and 2020, Reuters reports.

Rules for financial institutions to report suspicious activity to regulators have been in place for years, but cash real estate transactions have generally been exempt from those rules, according to Reuters.

The draft proposal sends a message that the U.S. will close off options for criminals looking to hide money in the country's real estate markets, Ian Gary, executive director of the Financial Accountability and Corporate Transparency Coalition, said in a press release.

“It is imperative that Treasury now finalize strong, permanent rules to prevent the misuse of U.S. residential and commercial real estate by foreign and domestic criminals, sanctioned Russian oligarchs, drug traffickers, sponsors of international terrorism, and other bad actors," Gary said.

Treasury officials also intend to release a separate rule to combat money laundering in U.S. commercial real estate markets later this year as the Biden administration continues to implement its 2021 Strategy on Countering Corruption. The strategy identifies specific anti-money laundering reforms as key national security objectives.

“By finalizing strong anti-money laundering safeguards for the multi-trillion dollar real estate sector, the Biden administration can live up to its commitments and catapult the United States from being a laggard to a leader in the global fight against corruption and illicit finance," Transparency International U.S. Executive Director Gary Kalman said in a statement.