The high court's agreement to hear the US Department of Justice's (DOJ) appeal in the debate over the Children's Internet Protection Act (CIPA) could set new standards for online speech.
The government has labelled CIPA a necessary step in protecting children from online pornography and other "harmful" content.
CIPA, which became law in 2000, requires public libraries to install "technological protection measures" on computers or risk losing some types of federal funding. A number of libraries, library patrons and civil liberty groups called the law unconstitutional.
The groups said the filtering requirement stifled free speech and served to deepen the digital divide, restricting Net access on computers used by people who often cannot afford to have them at home.
However, in May a three-judge panel in Pennsylvania agreed with the libraries and civil rights groups, ruling CIPA unconstitutional.
The panel said that the law would "block access to substantial amounts of constitutionally protected free speech whose suppression serves no legitimate government interest."
The DOJ appealed the ruling, sending it to the Supreme Court. The high court is unlikely to decide on the case until next year.