WASHINGTON—The top communications regulator won support to pass contentious new rules for Internet traffic, a move likely to face legal challenges and create uncertainty about Internet regulation.

The Federal Communications Commission is set to approve on Tuesday Chairman Julius Genachowski's proposed rules governing net neutrality—a concept aimed at preventing Internet providers from interfering with web traffic.

The rules are expected to bar providers from discriminating against legal Internet traffic and require more transparency. They also would let broadband providers for the first time charge more to companies that want faster service for delivery of games, videos or other services.

Net neutrality has become a contentious issue as worries grow that large phone and cable companies are growing too powerful as Internet gatekeepers. Start-ups and small businesses that rely on the Internet to provide shopping, information or other services to consumers are particularly concerned.

The FCC has wanted to step in and act as an Internet traffic cop, but Congress has never given it clear authority to do so.