Boston Fed President Eric Rosengren is concerned Republican plans to reform government-backed mortgage companies, including Fannie Mae and Freddie Mac, could destabilize multifamily property markets.

Rosengren said GSEs hold or guarantee around 44% of all outstanding multifamily loans, and said any significant changes to those organizations' structure, especially ones that require them to reduce their holdings of multifamily loans, have the potential to shock the entire apartment sector, Bloomberg reports. Rosengren did agree that lawmakers should look into whether the current level of government-sponsored exposure is safe, but suggested reforms should be gradual.

Fannie Mae and Freddie Mac have been under government control since the financial crisis when the federal government bailed out the mortgage giants in 2008 for $187B, and transferred all profits to the U.S. Treasury despite the fact that the companies are still traded over-the-counter — a fact that Treasury Secretary Steven Mnuchin hopes will change.

Mnuchin has called for Fannie and Freddie to be privatized, and investors largely agree, considering Fannie and Freddie have paid a combined $266B to the Treasury since their bailout.