All aliens, natural or juridical, as well as foreign organizations are strictly prohibited from engaging directly or indirectly in all forms of trade union activities without prejudice to normal contacts between Philippine labor unions and recognized international labor centers: Provided, however, That aliens working in the country with valid permits issued by the Department of Labor and Employment, may exercise the right to self-organization and join or assist labor organizations of their own choosing for purposes of collective bargaining: Provided, further, That said aliens are nationals of a country which grants the same or similar rights to Filipino workers.