If the union understands why workers might be reluctant to give up the raise, if it agrees that the company's treatment of the employees for the "past two years" has been bad, then the union ought to fall on its sword to some degree in this.
As in, cut every member's dues by at least $25 per month until the raise kicks in next August. That would make up for one out of every four weeks' worth of raise lost. With a new contract in place anyway -- a very rubbery and shrinkable contract, it seems -- the local chapter ought to be in position to do some belt-tightening. What's bad for the members needs to be bad for the chapter, too.