the federal government to prevent legal services providers who receive federal funds from seeking to “amend or otherwise challenge existing welfare law.”  Velazquez, 531 U.S. at 537.  On the other hand, the Supreme Court has held that it does not violate the First Amendment for the federal government to require healthcare providers who receive federal funds not to “encourage, promote or advocate abortion as a method of family planning,” Rust, 500 U.S. at 180; for the federal government to subsidize charitable organizations only if they do not engage in lobbying activity, see Regan v.  Taxation with Representation, 461 U.S. 540 (1983); and for the National Endowment for the Arts, in awarding grants on the basis of artistic excellence, to “take into consideration general standards of decency and respect for the diverse beliefs and values of the American Public.”  NEA v.  Finley, 524 U.S. 569, 572 (1998).  In light of the facts that we discuss above regarding the operation of public libraries, and the limits of Internet filtering software, see supra Sections ii.D-E, we believe that the plaintiffs have a good argument that this case is more analogous to League of Women Voters, Arkansas Writers’ Project, and Velazquez than it is to Rust, Finley and Taxation with Representation.  Like the law invalidated in League of Women Voters, which targeted editorializing, and the law invalidated in Arkansas Writers’ Project, which targeted general interest magazines but not “religious, professional, trade, and sports journals,” the law in this case places content-based restrictions on public libraries’ possible First Amendment right to provide patrons with access to constitutionally protected material.  See Arkansas Writers’ Project, 481 U.S. at 229 ("[T]he basis on which Arkansas differentiates between magazines is particularly repugnant to First Amendment principles:  a magazine’s tax status depends entirely on its content.  Above all else, the First Amendment means that government has no power to restrict expression because of its message, its ideas, its subject matter, or its content.”) (internal quotation marks and citations omitted); League of Women Voters, 468 U.S. at 383 ("[T]he scope of [the challenged statute’s] ban is defined solely on the basis of the content of the suppressed speech.").  See generally Rosenberger, 515 U.S. at 828 ("It is axiomatic that the government may not regulate speech based on its substantive content or the message it conveys.").  Because of the technological limitations of filtering software described in such detail above, Congress’s requirement that public libraries use such software is in effect a requirement that public libraries block a substantial amount of constitutionally protected speech on the basis of its content.  Plaintiffs’ argument that the federal government may not require public libraries who receive federal funds to restrict the availability of constitutionally protected Web sites solely on the basis of the sites’ content finds further