In an attempt to solve affordability issues in the housing market, the White House is said to have specified which firms President Trump's ban on investors buying homes plans to target.

The White House proposed banning investors with more than 100 single-family homes from purchasing more, in a memo sent to House and Senate committee leaders, the Wall Street Journal reported Thursday.

The number is far fewer than the 1,000-home cap some expected, and hoped for. Mega investors, those that own 1,000 or more properties, made up just 2.8% of single-family home purchases in December, but the new limit opens up the ban's impact to an additional 3% of the market, according to a recent Cotality report.

"The President has made it clear that he is committed to signing legislation that truly makes purchasing a home affordable again, and a key ingredient is his popular proposal to ban large institutional investors from purchasing single-family homes," White House spokesman Davis Ingle said.

But the White House plan offered various exceptions, such as for investors who build or heavily renovate homes to specifically rent them out. The proposal gives the Treasury secretary the ability to modify any of the criteria, like what exemptions to include, the Wall Street Journal reported. 

An exemption like this is important to maintain the cost advantages of renting, but is also the reason why some believe it won't have a significant impact on the market and affordability.

"This proposed ban will severely limit Americans' access to quality, affordable single-family rental homes and do little to impact the affordability crisis affecting American families," said Jake Keating, cofounder and partner at Backyard Ventures and former head of investments and strategy at Promise Homes. "Housing affordability is fundamentally a supply issue, and cutting off investor participation without taking into consideration all the market data and impact risks cutting off the crucial capital that's needed to fill an estimated 4 million housing unit gap."

The proposal does not require investors who exceed the cap to sell their homes as well, which will cause limited near-term effects on single-family rental securitizations, Fitch Ratings said.

The White House has been pushing to have the ban included in either of the major housing legislations moving through the House and the Senate, but the House passed the Housing for the 21st Century Act without the ban last week.

Trump is now pressing for the ban to be included in a new version of the Senate bill passed last fall, according to the Wall Street Journal. 

"The effort to ban large institutional investors from purchasing single-family homes has strong support among the American public, as well as Republicans and Democrats, enough for it to easily become law," Ingle said. "The White House is pleased with the collaboration coming from both chambers and both sides of the aisle as Congress works toward enactment of a housing package."