I just finished talking with K. Kajohnsak, VP-Legal on this issue. He gave me some information that actually it is not a must as you mentioned.
He did talk with both VN legal (Sorry!, I couldn't remember his name ) and K. Taweesak about this issue and let Ms. Mai to discuss with her legal team for finding solution. However, he still insisted certainly not agree if the Trade Union Established in the company athough the company will get fine