WASHINGTON—Internet service providers will have their business practices scrutinized for “digital discrimination” based on income or race under a regulation that was adopted Wednesday by the Federal Communications Commission, raising legal risks for some of America’s most powerful companies.  

The new rule lays the groundwork for the FCC to hold providers such as AT&T or Comcast liable if their actions “differentially impact consumers’ access to broadband”—intentionally or not. That will include decisions about network upgrades, pricing, marketing, maintenance and more.