Internet-service providers including AT&T, Verizon Communications and Comcast promised to take a more active role in fighting online piracy in an agreement with the entertainment industry announced Thursday.

The ISPs, which also include Time Warner Cable and Cablevision Systems, will send as many as six electronic alerts to customers whose accounts are purportedly being used to download or distribute illegal movies, television shows or music, according to a news release.

Customers who receive repeated alerts may have their Internet speed temporarily reduced, or have their Web access restricted until they discuss the matter with their Internet-service provider or review “educational” information about copyrights, according to a fact sheet about the program.

Internet subscribers may request an independent review before any restrictions are imposed under the agreement. The system is aimed at pirated music, movies and other content shared through online peer-to-peer networks.

The program, a voluntary set of industry best practices, is backed by trade groups representing the entertainment and media industries, including the Motion Picture Association of America, the Recording Industry Association of America and the National Cable & Telecommunications Association.

Verizon general counsel Randal Milch said the alert system is “designed to notify and educate customers, not to penalize them” and is aimed at informing customers about copyright laws and encouraging them to obtain content from “the many legal sources that exist.”

Piracy of digital movies, music and software cost businesses from $30 billion to $75 billion in 2008 in the Group of 20 leading global economies, according to a February report commissioned by the International Chamber of Commerce from Frontier Economics, a London-based consulting firm.