ATLANTA -- The union that represents Northwest Airlines ( NWA) flight attendants is suing Delta Air Lines ( DAL) to block the world's biggest carrier from starting the process to integrate the two carriers' seniority lists until the combined group is given the opportunity to vote on union representation. Northwest's 8,000 flight attendants are represented by the Association of Flight Attendants-CWA, while Delta's 14,000 flight attendants are not part of any union. Atlanta-based Delta bought Northwest for $2.8 billion in stock on Oct. 29. Federal rules allow for a post-merger union election involving workers from two different airlines if, among other things, it is determined that a single carrier exists. But in its suit filed in U.S. District Court in Washington on Friday, the AFA-CWA said it has not yet filed its application with the National Mediation Board seeking a single carrier determination that would prompt a union representation vote. It noted Delta has not yet obtained a single operating certificate from the FAA. Therefore, the AFA-CWA said efforts by Delta to start the seniority integration process are premature. The lawsuit cites a Nov. 11 letter from Michael Campbell, Delta's executive vice president of human resources and labor relations, to the head of Northwest's chapter of the AFA-CWA in which Campbell suggested having an initial seniority list integration meeting in early December between Delta, the AFA-CWA and a group of 14 Delta flight attendants who would represent all pre-merger Delta flight attendants. "By initiating the seniority integration process prior to NMB resolution of the representation matter, Delta seeks to force AFA to take a position which may benefit pre-merger Northwest flight attendants to the detriment of the unrepresented Delta workforce and thereby influence the unrepresented Delta flight attendants in an effort to induce them not to vote for AFA in the event of a representation dispute," the lawsuit says.