The airline industry's leading trade group is suing to stop the Obama administration from enforcing a new rule making it easier for unions to organize workers at airlines and railroads.

The Air Transport Association says the rule overturns 75 years of history with no compelling reason. The lawsuit in federal district court also claims the rule violates federal law.

The rule announced last week would recognize a union if a simple majority of workers who cast ballots agree to unionize. The old rule required a majority of the entire work force to favor unionizing. That meant workers who didn't vote were counted as "no" votes.

The rule was changed in a 2-1 vote by the National Mediation Board.