Sen. Elizabeth Warren sent letters to 14 major corporate landlords probing their business practices as her focus on rental industry regulation expands to multifamily and manufactured housing.

Warren, a Democrat from Massachusetts, implied that institutional investors threaten housing affordability and security as their holdings of apartment and manufactured housing communities have increased in recent years. The assertions were immediately challenged by commercial real estate professionals, including rental housing economist Jay Parsons, who said the letters include misleading and out-of-context claims that may sound scary to anyone not “well-versed on these topics.”

And they could have the opposite of the intended effect on affordability, he said.

“Rents are flat-to-falling across the country for 3+ years, largely due to large investors pushing the biggest supply wave in a half-century,” Parsons said in a Friday post. “But you won’t find that context in the letters.”

Warren’s Friday letters follow the Senate's passage of the 21st Century Road to Housing Act, including significant restrictions on institutional investment in single-family homes and a provision opponents say would kill build-to-rent housing development.

Although the Road to Housing Act passed the Senate by an 89-10 margin, Republicans still control the majority of both chambers, likely limiting the impact of Warren’s new inquiries.

Warren sent letters to investors including Blackstone, Greystar, Impact Communities, MAA, Starwood Capital and Tricon. They attempt to gather information about the landlords’ housing inventories, rental rates, business practices and communication with the Trump administration “regarding the role of institutional investors in the single-family, multifamily, and manufactured housing sectors.”

Some of the 31 questions in the letters get quite granular. One requests the number of maintenance requests and complaints filed by residents of each landlord’s single-family housing units for each year from 2020 to 2025, as well as a description of the nature of each complaint.

Warren requested detailed responses by April 8.

The letters express concern about corporate landlords and institutional investors making the housing crisis worse by buying more and more homes across sectors. In 2022, 32 institutional investors owned 450,000 single-family homes in the U.S., and they have acquired a 10% share of the multifamily market, totaling about 2.2 million units, Warren wrote.

Parsons said the 32 institutional investors’ 450,000 homes account for 0.5% of the market, underscoring the persistent fragmentation of the single-family home industry that the Road to Housing Act so heavily targets.

MSCI Real Capital Analytics data also shows that the average price per apartment unit in 2025 was $224K, which naturally limits the pool of 100-plus-unit-complex buyers to private equity or public REITs, Parsons said.

A Road to Housing Act provision forcing developers to sell BTR housing units within seven years of building them would “effectively shut down BTR development, leading to less supply and fewer options for renters,” the Mortgage Bankers Association and 11 other groups wrote in a letter this month.

A similar perceived risk for the apartment market “could have devastating impacts on apartment supply going forward — which will only further drive up rents,” Parsons said.