I'm the teacher that took an international school to court & won severance for 10 years service. They offered reduced benefits after I became a Thai citizen so I refused to sign the contract. There is a Supreme Court precedent about a group of expat teachers in Pattaya who won a case against an international school for non renewal of contract. I posted it here before. Unfortunately constructive dismissal isn't covered by Thai labour law. See out the contract & if it isn't renewed take them to court.