Amazon.com Inc. for years have successfully deflected attempts by its US employees to unionize. Now the tech company is preparing for a labor battle unlike ever before in its history.In the following two months, Thousands of Amazon employees at an Alabama warehouse are set to cast mail-in ballots over whether to organize into a union, a vote that could redefine the relationship between workers and the nation’s second-biggest employer.The commerce behemoth faces a familiar opponent: the Retail, Wholesale and Department Store Union, or RWDSU, which along with local organizers is supporting in leading the pro-union campaign. The union has supported in organizing thousands or poultry workers in Alabama, a right-to-work state, and has ended up a frequent Amazon antagonist in recent years. The RWDSU fought the company’s plans for a second headquarters in New York in late 2018 and helped the worker protests at some warehouses during the coronavirus pandemic.So far, the current effort has had more success to organize Amazon workers, according to the labor experts. They note that a successful union push at the warehouse could cause similar actions at Amazon’s more than 800 facilities in the US.