http://www.dtic.mil/whs/directives/corres/html2/d13341x.htm

Wearing Military uniforms is prohibited in the following situations:

In connection with the furtherance of any political or commercial interest, or when engaged in off duty civilian employment.

When participating in public speeches, interviews, picket lines, marches, rallies, or public demonstrations, except as authorized by competent authority.

When attending any meeting or event that is a function of, or is sponsored by, an extremist organization.
When wearing the uniform would bring discredit upon the Army.

When specifically prohibited by Army regulations.


Retiree Uniform Restrictions:

Wear of the member's uniform is prohibited for all retirees:

In connection with the promotion of any political or commercial interests or when engaged in off duty civilian employment. Reserve technicians who are also members of the Ready Reserve may wear their uniform at their option while on duty in their civil service status.

When participating in public speeches, interviews, picket lines, marches, rallies, or public demonstrations, except as authorized by competent authority.

When wearing the uniform would bring discredit upon the Uniformed Services.

When specifically prohibited by DoD Regulations.