The Air Transport Association on Monday filed a federal suit against the National Mediation Board, seeking to block a change to a 75-year-old rule governing union elections. The NMB "has offered no adequate or neutral justification for this sweeping rule change," ATA said in its suit, which was joined by several member airlines. The NMB violated its own procedures and discriminated against workers by failing to allow for decertification under the new rule, according to the suit. The rule is scheduled to go into effect on June 10, but ATA said it will seek a preliminary injunction while its suit is pending. "By altering how the question of union representation is resolved in the airline industry, and by permitting the certification of minority-supported unions, the NMB's new rule will likely fundamentally change the legal duties and relationships between many ATA- member airlines and their employees," the association said.