A split over the stewardship of the union’s high-profile president, Christian Smalls, has led a rival faction to file a lawsuit seeking an election.A dissident group within the Amazon Labor Union, the only certified union in the country representing Amazon employees, filed a complaint in federal court Monday seeking to force the union to hold a leadership election.The union won an election at a Staten Island warehouse with more than 8,000 employees in April 2022, but Amazon has challenged the result and has yet to begin bargaining on a contract.The rise of the dissident group, which calls itself the A.L.U. Democratic Reform Caucus and includes a co-founder and former treasurer of the union, reflects a growing split within the union that appears to have undermined its ability to pressure Amazon. The split has also threatened to sap the broader labor movement of the momentum generated by last year’s high-profile victory.In its complaint, the reform caucus argues that the union and its president, Christian Smalls, illegally “refuse to hold officer elections which should have been scheduled no later than March 2023.”The complaint asks a federal judge to schedule an election of the union’s top officers for no later than Aug. 30 and to appoint a neutral monitor to oversee the election.Mr. Smalls said in a text message Monday that the complaint was “a ridiculous claim with zero facts or merit,” and a law firm representing the union said it would seek legal sanctions against the reform group’s lawyer if the complaint was filed.The complaint states that under an earlier version of the union’s constitution, a leadership election was required within 60 days of the National Labor Relations Board’s certification of its victory.But in December, the month before the labor board certification, the union’s leadership presented a new constitution to the membership that scheduled elections after the union ratifies a contract with Amazon — an accomplishment that could take years, if it happens at all.On Friday, the reform caucus sent the union’s leadership a letter laying out its proposal to hold prompt elections, saying it would go to court Monday if the leadership didn’t embrace the proposal.The reform group is made of up more than 40 active organizers who are also plaintiffs in the legal complaint, including Connor Spence, a union co-founder and former treasurer; Brett Daniels, the union’s former organizing director; and Brima Sylla, a prominent organizer at the Staten Island warehouse.The group said in its letter that enacting the proposal could “mean the difference between an A.L.U. which is strong, effective, and a beacon of democracy in the labor movement” and “an A.L.U. which, in the end, became exactly what Amazon warned workers it would become: a business that takes away the workers’ voices.”Mr. Smalls said in his text that the union leadership had worked closely with its law firm to ensure that its actions were legal, as well as with the U.S. Labor Department.Jeanne Mirer, a lawyer for the union, wrote to a lawyer for the reform caucus that the lawsuit was frivolous and based on falsehoods. She said that Mr. Spence had “improperly and unilaterally” replaced the union’s founding constitution with a revised version in June 2022, and that the revision, which called for elections after certification, had never been formally adopted by the union’s board.Retu Singla, another lawyer for the union, said in an interview that the constitution was never made final because there were disagreements about it within the union’s leadership.Mr. Spence said he and other members of the union’s board had revised the constitution while consulting extensively with the union’s lawyers. A second union official involved in the discussions corroborated his account.The split within the union dates from last fall, when several longtime Amazon Labor Union organizers became frustrated with Mr. Smalls after a lopsided loss in a union election at an Amazon warehouse near Albany, N.Y.In a meeting shortly after the election, organizers argued that control of the union rested in too few hands and that the leadership should be elected, giving rank-and-file workers more input.The skeptics also complained that Mr. Smalls was committing the union to elections without a plan for how to win them, and that the union needed a better process for determining which organizing efforts to support. Many organizers worried that Mr. Smalls spent too much time traveling the country to make public appearances rather than focus on the contract fight on Staten Island.Mr. Smalls later said in an interview that his travel was necessary to help raise money for the union and that the critics’ preferred approach — building up worker support for a potential strike that could bring Amazon to the bargaining table — was counterproductive because it could alarm workers who feared losing their livelihoods.He said a worker-led movement shouldn’t turn its back on workers at other warehouses if they sought to unionize. A top union official hired by Mr. Smalls also argued that holding an election before the union had a more systematic way of reaching out to workers would be undemocratic because only the most committed activists would vote.When Mr. Smalls unveiled the new union constitution in December, scheduling elections after a contract was ratified, many of the skeptics walked out. The two factions have operated independently this year, with both sides holding regular meetings with members.In April, the reform caucus began circulating a petition among workers at the Staten Island warehouse calling on the leadership to amend the constitution and hold prompt elections. The petition has been signed by hundreds of workers at the facility.The petition soon became a point of tension with Mr. Smalls. In an exchange with a member of the reform caucus on WhatsApp in early May, copies of which are included in Monday’s legal complaint, Mr. Smalls said the union would “take legal action against you” if the caucus did not abandon the petition.The tensions appeared to ease later that month after the union leadership under Mr. Smalls proposed that the two sides enter mediation. The reform caucus accepted the invitation and suspended the petition campaign.But according to a memo that the mediator, Bill Fletcher Jr., sent both sides on June 29 and that was viewed by The New York Times, the union leadership backed out of the mediation process on June 18 without explanation.“I am concerned that the apparent turmoil within the ALU E. Board means that little is being done to organize the workers and prepare for the battle with Amazon,” Mr. Fletcher wrote in the memo, referring to the union’s executive board. “This situation seriously weakens support among the workers.”Colin Moynihan More