Chapter III : Neutral persons - Art. 17.
Art. 17 A neutral cannot avail himself of his neutrality
(a) If he commits hostile acts against a belligerent;
(b) If he commits acts in favor of a belligerent, particularly if he voluntarily enlists in the ranks of the armed force of one of the parties.
In such a case, the neutral shall not be more severly treated by the belligerent as against whom he has abandoned his neutrality than a national of the other belligerent State could be for the same act.