How worried should I be?

So I removed a student from my lesson today for being rude and disruptive to other students. He then accused me of being a liar during a restorative conversation afterwards and refused to own up to his behaviour. I got angry with him and said to him “how dare you accuse me of lying to you. You never speak to a teacher like that ever.” I then spoke to his mother on the phone afterwards and she said she’s arranging a meeting with the school to speak about it and that my behaviour is unacceptable. How screwed an I and can this be used to justify a dismissal? Should I be contacting my union now?