Not being an attorney, I can't say whether there is a legal basis for action or not, but as a member of the Union I think we should start exploring that avenue with an eye to both the Labor board and the Company. Sue the Union? Why would you even think of doing that? We have the means to change the Union by the members acting in accordance with the bylaws.

Without an external force acting on the Company it is a fact proven over time that they will stonewall any effort at negotiations. That external force can come from the Labor board(with proper legal motivation), other components of company labor, legal action against the company(once an effort is made to develop a legal strategy), or economic concerns(IRO, crew productivity, scope, etc.).
The current course of action is NOT working, it's time for a new strategy. I would rather my dues be spent on an exploration and implementation of possible legal action instead of another collection of useless pins and lanyards.