"5. RESERVE/GUARD MEMBERS. According to AFI 36-2907, IC 2005-1, para. 3.1, commanders, supervisors, and other persons in authority can issue administrative counselings, admonitions, and reprimands to reservists who commit an offense even while in civilian status. Under AFI 36-2907, para. 3.5.1.4, non-EAD reservists have 30 calendar days from the date of receipt of the certified letter to acknowledge the notification, intended actions, and provide pertinent information before the commander makes a final decision....AFI 36-2907 does not apply to Air National Guard (ANG) members. Many state codes of military justice authorize letters of admonition or reprimand. There is no AFI or ANGI that addresses the issuing of counselings, admonitions, and reprimands to ANG members; however, commanders and supervisors have inherent authority to do so. Consult your local staff judge advocate before issuing an LOC, LOA or LOR to an ANG member."
I had to do this once to a reservist in civilian status several years ago, so it was fresh on my mind. We had to consult the Texas UCMJ regarding NG members since the UCMJ didn't apply. However, according to the AFI...a reservist can be given an LOR even in civilian status. When it comes to guardsmen...you have to consult the State laws. I would imagine most states give commanders the authority. There has to be a way to punish conduct unbecoming...DWI...etc.
You are more than welcome to a copy of the guide. FREEPMAIL me with your email and I'll send it to you via my .mil
AR 27-10 (Page 108)
Chapter 20-2b
“The ARNG Soldiers are not subject to the UCMJ while in State service under 32 USC (Title 32).”
http://www.apd.army.mil/pdffiles/r27_10.pdf