http://www.aclu-wa.org/news/street-s...et-and-leaflet :
Airports, Train Stations and Ferry Terminals
People may exercise their free speech rights in the public areas of airports11. Nevertheless, airport officials may impose reasonable restrictions on the time, place, and manner in which the rights are exercised.
For example, speech activity may be prohibited where there is a captive audience or where it interferes with the normal use of the airport facility. Also, a temporary ban on speech may be justified in emergency situations, but the ban must last no longer than the emergency.
Officials may not impose regulations that are arbitrary or unreasonable. They may not require people to register in advance with airport officials for peaceful leafleting, picketing and communication. However, you may have to register in advance for large-scale activities, such as rallies, where the activity may be disruptive. You may also have to register in advance to ask for donations.