Fox Broadcasting plans to make its recently aired TV episodes available on the Web only to paying subscribers, a new step as major broadcast-TV networks consider reining in free Web offerings that could undermine their traditional advertising and subscription businesses.

Beginning in mid-August, new episodes of Fox shows, including "Glee" and "Family Guy," will no longer be available to watch free on Fox.com or video site Hulu until eight days after they debut, Fox says. To watch before that, viewers will need to prove they...