The union that successfully organized an Amazon warehouse in New York is being sued by some former members who claim the union is violating its own constitution. The complaint, filed Monday in U.S. District Court of the Eastern District of New York, comes as the upstart Amazon Labor Union struggles to capture the momentum that led to its surprising victory last year following a series of setbacks. In the complaint, a splinter group, which calls itself A.L.U. Democratic Reform Caucus, argues the union amended its constitution in December to make changes that would delay when officer elections would be held. It's asking the court to step in and force an election on or before August 30. An attorney for the union has called the claims frivolous.