Failure to represent?

[jp102]

I work for a 911 dispatch center as part of a sheriff's dept and we belong to the same union as all of the deputies. The bargaining unit has around 1200 members, 40 of them are dispatchers. With the last contract, our union for all intents and purposes completely disregarded the dispatchers and failed to even ask for financial compensation that would bring us up to the average pay in the county. The union then held special meetings with the dispatchers where they acknowledged that the "dropped the ball" and promised to attempt to secure in the next contract, what we had asked for on that contract. Jump forward 2 yrs -- we are now back to negotiating for a new contract. Dispatch was very optimistic because the union had promised that this new contract was "our contract" and again said they intended to remedy their last, admitted failure/mistake. The union rep came into dispatch a number of times and polled the dispatchers as to what their top concerns were for this contract. Every single dispatcher said they wanted pay equal to the deputies working in the corrections division. A few weeks back, the union had a general membership meeting to discuss what was being asked for at the negotiating table. When asked why dispatch/deputy pay parity wasnt on the table, they told us "you wont get the same pay as a d1 (corrections dep) so stop asking for it." This obviously shocked all of us, as they had been promising it to us for over 2yrs. Its this just cause for action with our state (michigan) against our union for failure/refusal to represent us?