Owners of National Football League teams would have to approve any franchise moves under legislation introduced Thursday by Sen. Dianne Feinstein, who hopes to keep the 49ers from leaving San Francisco.

The measure, called the Football Fairness Act of 2007, would grant professional football a limited antitrust law exemption, which Feinstein said is needed because football teams are so important to their hometowns. Antitrust laws typically prevent business owners from colluding as a group to limit competition.

Feinstein has said she would consider writing legislation to block the 49ers from using the words "San Francisco" or "49ers" in their name if they left the city. Spokesman Scott Gerber said Thursday the senator is still studying the idea.