I seriously doubt that they have a case against ALPA.
Interestingly, ALPA would have a BETTER case against all these "7 Check Airmen" who went out and busted pilots on line checks that were vocal against the contract within a week after the TA failed. Remember, there were over 50 pilots that failed line checks who had never failed a training event in their career. They went after the vocal ones. This is clear and obvious evidence that the Fantastic 7 Check Airmen were outrageously mad when they did not receive their signing bonus or their jelly of the month club membership (didn't get either of 'em).
There's a stronger case for ALPA to go after these check airmen goons who deliberately and un-reasonably failed people who voted NO. Especially now that they have made it public that they are outraged they didn't get their bonus.
So which Check Airmen is leading the lawsuit?