What political activities are members of the Armed Forces permitted to do?
A member on active duty may:
Register, vote, and express a personal opinion on political candidates and issues, but not as a representative of the Armed Forces.
Promote and encourage other military members to exercise their voting franchise, if such promotion does not constitute an attempt to influence or interfere with the outcome of an election.
Join a political club and attend its meetings when not in uniform. See Directive 1334.1.
Serve as an election official, if such service is not as a representative of a partisan political party, does not interfere with military duties, is performed when not in uniform, and has the prior approval of the Secretary concerned or the Secretary's designee.
Sign a petition for specific legislative action or a petition to place a candidate's name on an official election ballot, if the signing does not obligate the member to engage in partisan political activity and is done as a private citizen and not as a representative of the Armed Forces.
Write a letter to the editor of a newspaper expressing the member's personal views on public issues or political candidates, if such action is not part of an organized letter-writing campaign or a solicitation of votes for or against a political party or partisan political cause or candidate.
Make monetary contributions to a political organization, party, or committee favoring a particular candidate or slate of candidates, subject to the limitations under 2 U.S.C. 441a, 18 U.S.C. 607 and other applicable law.
Display a political sticker on the member's private vehicle.
Attend partisan and nonpartisan political meetings or rallies as a spectator when not in uniform.
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Source: http://www.ig.navy.mil/complaints/Complaints%20%20(Political%20Activities%20of%20Military%20Members).htm