10. Adarna Manufacturing Company (AMC) and Adarna Employees Union (AEU) entered into collective bargaining negotiations but reached an impasse. AEU then filed a notice of strike before the National Conciliation and Mediation Board, which immediately conducted conciliation meetings to avert the strike. Fifteen days after the filing of the notice, and despite the conciliation proceedings, AEU staged a strike with the participation of 50% of its members. Is the strike legal? Briefly explain.