US President Donald Trump has announced plans to ban large corporate investors from buying single-family homes in an effort to make housing more affordable for Americans.

In a social media post Wednesday, President Trump asked Congress to “codify” the plan and said he would discuss it further at the Davos World Economic Forum later this month.

The pledge reinforced a long-standing belief among housing advocates and lawmakers in response to Wall Street’s growing role in the U.S. housing market. But some analysts question how much the ban will affect prices.

Shares in Blackstone, one of private equity’s biggest buyers, fell more than 5% on Wednesday.

President Trump addressed homeownership on social media, saying, “The American Dream is increasingly out of reach for too many people, especially young Americans.”

“People live at home, not at work.”

The White House did not immediately respond to a request for comment on the specifics of the ban, including whether it would require Congressional approval.

President Trump’s comments on Wednesday came as his administration faces growing public pessimism about its handling of the economy. In recent weeks, he has sought to allay voters’ concerns about the cost of living in the United States, saying housing affordability is at the top of Americans’ concerns.

Sam Garlin, a spokesman for an advocacy group that warns about the impact of private equity ownership on renters, said the organization welcomed Trump’s move.

“We await the details of what this policy actually entails,” said Garin of the Private Equity Stakeholder Project, adding, “But we urge policymakers not to stop there.”

Since the 2008 financial crisis triggered a wave of foreclosures, Wall Street investors such as Blackstone and other private equity firms have bought tens of thousands of homes and rented them out, becoming major landlords in certain markets in particular.

That role has drawn scrutiny from lawmakers in both parties, who have accused the companies of helping drive up rental and purchase costs. But previous legislative efforts have had little traction.

“Senate Democrats tried to do this last year, but Republicans blocked it,” Senate Democratic Leader Chuck Schumer said on social media.

Sen. Bernie Moreno, R-Ohio, said Wednesday he would introduce legislation to codify Mr. Trump’s proposal.

Shares of real estate companies fell on Wednesday following President Trump’s comments. Building materials supplier Builders FirstSource fell more than 5%, and single-family home owner Invitation Homes fell 6%.

But some housing industry analysts doubt the ban will hit home prices too hard, given the relatively small role of institutional investors in the overall market.

Laurie Goodman, a fellow at the Urban Institute, said the impact of the ban will depend in part on how “large” investors are defined.

Blackstone said the agency owns 0.5% of all single-family homes in the United States.

Goodman said her research found that institutional investors, defined as investors who own at least 1,000 units in three or more locations, own about 4% of the single-family market.

This number has remained stable over the past few years as high interest rates and soaring home prices have slowed purchases, he added.

Goodman said the proposed ban also raised other questions, including how existing real estate owned by institutional investors would be treated.

He said that instead of an outright ban, “institutional investors should be required to provide more capital to tenants.”

Darryl Fairweather, Redfin’s chief economist, warned that if large investors are barred from buying single-family homes, they will likely be replaced by smaller investors rather than first-time homebuyers.