Is it right to tell interview that you filed a labor case against your previous employer?

Don't tell them. That's not something they have a right or obligation to know. All they are obligated to know is that you used to work at a particular job. In fact, if you tell them your work history and consent to them calling a previous employer all they can legally ask is if you used to work there. It will just look bad if you bring up dirt on any previous employer.