International law, to which the United States are signatories:
"Pepper spray is banned for use in war by Article I.5 of the Chemical Weapons Convention which bans the use of all riot control agents in warfare whether lethal or less-than-lethal."
http://en.wikipedia.org/?title=Pepper_spray#Legality
http://en.wikipedia.org/wiki/Chemical_Weapons_Convention
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The Geneva Conventions:
Art 76. Protection of women
1. Women shall be the object of special respect and shall be protected
in particular against rape, forced prostitution and any other form of
indecent assault.
Art 77. Protection of children
1.
Children shall be the object of special respect and shall be protected
against any form of indecent assault. The Parties to the conflict shall
provide them with the care and aid they require, whether because of
their age or for any other reason.
http://www.icrc.org/ihl.nsf/full/470?opendocument
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What happened:
30 Pepper-Sprayed Outside Santa Monica College Board of Trustees Meeting
About 30 students were treated for pepper spray, and two were transported to the hospital.