Schools and libraries that receive federal funds will find new strings attached to the money -- they'll have to filter Internet content. An amendment attached to a sweeping appropriations bill that Congress passed Friday would require most of the nation's public schools to block visual depictions of child pornography, obscenity, or other material deemed inappropriate for children. But free speech advocates already are planning lawsuits to challenge the measure, which they say violates the First Amendment. "It's a violation by censoring what adults can view in a library," said Ann Beeson, an ACLU staff attorney. She said the measure was "[similar to] Congress asking for an entire type of book removed from a library, which it hasn't done before". In the past, the ACLU has successfully blocked free-speech threatening amendments that had been attached to appropriations bills, including the Communications Decency Act. The legislation that passed Friday is the culmination of two years of negotiations by proponents of filtering mandates and others who fear they might be overly restrictive. Even filtering companies -- which stand to make millions if the new measure stands -- have reservations about the new bill. David Crane, an aide to senator John McCain (Republican, Arizona), one of the measure's sponsors, said the bill is intentionally broad, leaving local communities and schools to pick their own technology and define terms such as "obscenity". The FCC, charged with enforcing the law, cannot force its definitions of inappropriate materials on others, according to Crane. "It is entirely up to local authorities. You decide what you want blocked and how you want it blocked." The Labour, Health and Human Services, and Education Appropriations Bill (HR 4577), now headed to the president's desk for signature, gives schools and libraries 120 days to present their filtering plans to the federal government. Filtering software is designed to block material deemed inappropriate for children, such as sites containing violent or pornographic images. However, critics complain the software often goes too far, unintentionally banning sites that are neither offensive nor controversial. In recent months, free speech group Peacefire.org has shown that some software blocks content that many educators probably would want children to see, including the Web sites of some Congressional candidates and pages of Amnesty International. Even filtering companies -- which stand to make millions if the new measure stands -- have reservations about the new bill. Nika Herford, a spokesman for Net Nanny Software International Inc., said the new rules will require that some filtering products be revamped, since it specifically applies to visual depictions. "That right there is somewhat problematic," said Herford, who explained that while Net Nanny software can block images, singling out pornographic images will be a challenge. "And then what do you do about fine art?" What's more, she said it would be difficult for companies to design products that can adapt to meet the standards of communities as diverse as California and, say, the Bible Belt. "The legislation is well-meaning, but may not necessarily have the outcome the people who wrote it hoped it would have," Herford said. Already several communities have rejected mandatory blocking software. Two years ago, in Loudoun County, Virginia, a judge ruled that a plan to install filtering software in the county's public library violated free speech. Last February, residents of conservative Holland, Michigan, voted against mandatory filtering in the nation's first referendum on the issue. Rob Courtney, a policy analyst at the Center for Democracy and Technology, said citizens there will now have to use filtering technology, like it or not. Many parents find filtering software packages useful, Courtney said, "But to mandate them in every community is to mandate their strengths as well as their shortcomings." Courtney said his group also might consider joining cases filed by groups such as the ACLU. "Once the legislative options have come up dry, litigation is the way to go," he said. ZDNet's Ben Charny also contributed to this report. Take me to the Web of Porn Special Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet News forum. Let the editors know what you think in the Mailroom. And read what others have said.