According to Ballot Access News:
In 2000, the Initiative & Referendum Institute filed a lawsuit against the U.S. Postal Service against a regulation passed that year that makes it illegal for petitioning to occur on post office sidewalks. The part of the case involving interior postal sidewalks is still in U.S. District Court in Washington, D.C. Recently, the judge in the case asked the postal service to send a survey to all postmasters, asking to what extent people have used interior postal sidewalks for First Amendment activity, including petitioning. The results should be known in a month. “Interior sidewalks” means sidewalks that lead from the street to the post office, or to its parking lot, or between the parking lot and the post office itself.