The ruling could have an impact on protests at all U.S. military facilities.
Vandenberg Air Force Base is in a rural area on the coast of central California, about 170 miles northwest of Los Angeles. The base is the site of sensitive missile- and space-launch facilities, and is generally closed to the public.
However, the base is crossed by two state roads that are open to the public.
Highway 1 runs next to Vandenberg's main gate. Near that gate, the base commander has designated an area for public protesting, which though part of the base, also falls within the scope of the Highway 1 easement.
Protester John Dennis Apel has twice been barred from Vandenberg, in 2003 for trespassing and vandalism and in 2007 for trespassing.
But in 2010, Apel entered Vandenberg three times, and each time was escorted off the base. He was convicted of three violations of a federal statute and ordered to pay $305 in fines and fees.
A federal appeals court ruled in his favor, saying the federal law governing protesters kicked out of a base "applies only to areas over which the federal government exercises an exclusive right of possession."
The U.S. Supreme Court threw out, or vacated, the appeals court ruling.
The prevailing opinion, written by Chief Justice John Roberts, said federal law law does not require "exclusive possession and control" for the Air Force to impose its rules. The rest of the court signed on to the opinion, or agreed with the judgment for different reasons.
The high court ruling sends the case back down to the lower court for a different result based on the opinion.