After years of organizing Amazon workers and pressuring the company to bargain over wages and working conditions, two prominent unions are teaming up to challenge the online retailer.

The partnership was made final in voting that ended on Monday after members of the Amazon Labor Union, the only union formally representing Amazon warehouse workers in the United States, voted overwhelmingly to affiliate with the 1.3-million-member International Brotherhood of Teamsters. The vote was overseen by the Amazon union.

The A.L.U. scored a surprise victory in an election at a Staten Island warehouse in 2022. But it has yet to begin bargaining with Amazon, which continues to contest the election outcome. Leaders of both unions said the affiliation agreement would put them in a better position to challenge Amazon and would provide the A.L.U. with more money and staff support.

“The Teamsters and A.L.U. will fight fearlessly to ensure Amazon workers secure the good jobs and safe working conditions they deserve in a union contract,” Sean O’Brien, the Teamsters president, said in a statement early Tuesday.

Amazon declined to comment on the affiliation.

The Teamsters are ramping up their efforts to organize Amazon workers nationwide. The union voted to create an Amazon division in 2021, and Mr. O’Brien was elected that year partly on a platform of making inroads at the company.

The Teamsters told the A.L.U. that they had allocated $8 million to support organizing at Amazon, according to Christian Smalls, the A.L.U. president, and that the larger union was prepared to tap its more than $300 million strike and defense fund to aid in the effort. The Teamsters did not comment on their budget for organizing at Amazon.