The U.S. Chamber of Commerce joined a federal lawsuit Monday against a new union organizing rule. The Chamber filed a motion to intervene as a party-plaintiff in the Air Transport Association’s (ATA) suit against the National Mediation Board (NMB). The business lobbying group opposes a rule change finalized by the board earlier this month that makes it easier for workers at companies covered by the Railway Labor Act to unionize. Under the rule, workers who don’t vote in a union election are not counted as votes either for or against forming a union. Such non-votes previously were counted as votes...