18 USC § 1507.
"Whoever, with the intent of interfering with, obstructing, or impeding the administration of justice, or with the intent of influencing any judge, juror, witness, or court officer, in the discharge of his duty, pickets or parades in or near a building housing a court of the United States, or in or near a building or residence occupied or used by such judge, juror, witness, or court officer, or with such intent uses any sound-truck or similar device or resorts to any other demonstration in or near any such building or residence, shall be fined under this title or imprisoned not more than one year, or both."
Law professor Eugene Volokh on this subject:
“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.”
(The United States Constitution, Amendment 1).