It could be that the reason that this is believed to profitable is that it would decrease demand for unionized employees thus reducing costs. This would be consistent with raising prices and decreasing supply after acquiring a substitute. Further, it could be a negotiation ploy by management to decrease union bargaining power. This is what the Allied Pilots Association (APA) is arguing:
"If permitted to expand their scope, immunized airline alliances may lead to increased foreign control of U.S. airline operations, including maintenance practices and crew training," the association said in a release.Alternatively, the lost jobs to feriners could be a red herring and union opposition is the negotiation ploy. The APA is levering potential political clout so as to maximize its share of any potential spoils.