A new law aims to make Wall Street investors feel unwelcome in the market for existing homes while urging them to build more supply. The 21st Century ROAD to Housing Act passed into law last week despite President Trump's refusal to sign it.

Under the law, investors who already own more than 350 family homes can't buy any more from the existing housing stock. This restriction targets large institutional investors who have been snapping up single-family homes.

There are exceptions. Investors can still buy homes needing extensive renovation that regular buyers avoid, and when tenants are offered a right to eventually own the house. The law attempts a tricky balancing act between curbing speculation and encouraging new construction.

Failure could push up rents by reducing capital for new supply. The legislation reflects growing concern over institutional investors' role in the housing market, though its impact remains uncertain.