This FHFA rule requires Fannie Mae and Freddie Mac “to maintain policies that promote aligned investor cash flows” for mortgage backed securities, codifying alignment requirements that FHFA implemented while Fannie and Freddie are in conservatorship. FHFA says this rule is integral to the successful transition to and ongoing fungibility of the Uniform Mortgage-Backed Security. Fannie and Freddie will begin issuing UMBS on June 3, 2019. They cover fixed-rate mortgages backed by single-family properties (defined as properties with one to four units).