HamburgToBKK

Hi fellow teachers, I need some input please. I am currently teaching at a Thai school for four years with wp and a proper recurring contract. So I got paid on Friday and it seems that the school deducted a daily wage from it because there was a public holiday on May 22nd. They have never done this before. I believe that this a violation of the Thai labour law. Am I right? Additional question: If a make a fuss and they fire me with due notice, am I entitled to severance pay?