In any of the normal (Europe 2nd Pacific 2nd Global40 2nd edition) games the attack on any true neutral, triggers all other true neutrals to become hostile towards the attacking force, f.e. if Germany attacks Spain, to go towards Gibraltar, All other true neutrals in South America or Africa and Middle east would become pro Allied, they could be taken in non combat movement.
I never have played a game with a Portuguese fleet, so I dont know which version that is, or what rules apply towards that game.