No, it's not. He has a duty to do so. At least, that is what we were taught while I was in the service. It's drilled into us from day 1 that there is no duty to obey an unlawful order, while there is a duty to disobey an unlawful order and report it up through the chain of command. The problem comes in when there is significant room for interpretation of an order when determining its lawfulness. Our training said that the first step should be up through the chain of command to verify legality; but in some cases, this is clearly not possible.
Personally, this should have been dealt with in the US, by US officials; but none of the recent administrations have had a particularly good track record regarding objectors and whistle blowers.