Under the Spending Clause, Congress cannot use its spending power to
"induce the recepient to engage in unconstitutional activity" (South Dakota v Dole).
Thus, if the Congress conditions a grant of money on the recipient
taking some action that would violate the First Amendment rights of
others, the action of Congress would be unconstitutional. (Note:
In U. S. v
American Library Ass'n, dissenting justices Ginsburg and Souter
argued that this principle was violated when Congress conditioned the
grant of money to public libraries on the libraries using filters to
block computer access to materials harmful to minors.)
2. The government cannnot use its dollars to promote favored speech (or restrict unfavored speech) when the speech is not "a governmental message" made as part of a government program (Legal Services Corporation v Velazquez). The use of dollars to promote favored speech is permissible, however, when the speakers are participants in a government program and are, therefore, "government speakers" (Rust v Sullivan).
3. The government cannot use its dollars to promote a particular viewpoint that is not related to a significant and legitimate government objective (Board of Education v Pico). Legitimate and significant objectives, in the case of a junior high school library might include not exposing students to graphically sexual materials, materials that condone drug use or violence, or materials that undermine educational objectives (Pico).