That would be a decertification. They're slightly different legally, but this is generally the point. Decert is supposed to show the members don't want the representation, whereas DOI is allowing a union that they elected to voluntarily leave for some reason without fault.
*shrugs*
Who knows, then?
The vote won't matter anyway. It'll pass. Only way DoI will be filed is if the negotiations go off the rails so badly that a deal isn't going to get done anyway.