The American Civil Liberties Union has posted a Web page that urges Internet users to express their opposition to an online FBI wiretapping system by faxing or e-mailing a prepared letter to members of Congress and the White House.

The FBI says "Carnivore" -- basically a computer running specialized software -- is set up on an Internet Service Provider’s network, searches through all of its users’ electronic messages (e-mail, instant messages and web addresses) -- looking for messages from someone suspected of committing a crime. The ACLU says the program is a threat to the privacy of all Americans.

"Never before has the FBI insisted that it has the authority to capture all of the communications passing through a network," Barry Steinhardt, the ACLU’s associate director, told the House Judiciary Committee’s Subcommittee on the Constitution. "Never before has a law enforcement agency asked for this kind of power based on an unsupervised promise that it will not stray beyond the confines of its authority."

Steinhardt urged Congress to adopt legislation upholding the Fourth Amendment’s protection against unwarranted searches. "Congress must send clear messages to the FBI," he stated. "Under no circumstances must it be allowed to engage in such a mass invasion of the privacy of law-abiding citizens."

The Web site offers links to information on "Cyber Liberties," tips on contacting elected officials and other civil liberties issues before Congress, among other items.