While I can understand the CSM’s desire to motivate Soldiers to acquire the ASU. He cannot legally require Soldiers to attend a board in an alternate uniform when the Class A’s are still authorized.
I would venture to say that if a Soldier filed a complaint with the local JAG or IG the chain of command would be some what embarrassed especially if the LOI for the board states something like the Soldiers must appear in the ASU and the Class A is not authorized. It may be wise to obtain a legal opinion from JAG and/or make an inquiry with your local IG. You can make both inquiries without providing a unit or names. If I am correct then the information obtained can be shared with the chain of command and they can determine if they desire to change their policy or if they are willing to receive complaints.