This question is complex and the Soldier needs to look at the information in this response then speak with their JAG if they are a member of the National Guard.
National Guard Soldiers
I spoke with a JAG source. If a Soldier is on Title 10 orders under federal activation, then it is definitely unlawful. However, if they are on Title 32 orders under state jurisdiction, then it may be legal. Each state has their own regulations for UCMJ imposition and what they can and cannot do. FOR EXAMPLE: If the Soldier says, no I’m not going to turn over my keys, the NG can say fine, you are out of the guard and release them. They can also face UCMJ action under the state guidelines they fall under.
I always thought the guard fell under the same UCMJ rules as the federal services, but that only applies if they are on federal (Title 10) orders.
Army Reserve Soldiers
Now, if these are reservists on Annual Training, then it is unlawful to take their car keys as they are always on Title 10 orders.
Active Duty Soldiers
Then the answer is this is absolutely illegal. It is unlawful search and seizure
What Can the Commander do?
The Commander can ordered Soldiers not to drive, enter, use, etc the car. Then Soldiers who violate the order can be punished for violating the order, but they cannot confiscate their keys.
Things to Consider
Consider presenting the issue to the chain of command in an effort to solve the issue at the lowest level of leadership. Be Professional, Factual, Calm, Unemotional. Consider presenting the alternatives above under “WHAT CAN THE COMMANDER DO? If this does not work consider ane IG complaint or a quick phone call to their servicing JAG would be appropriate.
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