Federal labor agency prosecutors have determined that Amazon is a joint employer of subcontracted drivers who delivered packages for the company in California, refuting the online retailer's claims that they are not its employees.

The decision, made by a regional director for the National Labor Relations Board in Los Angeles, followed an investigation into unfair labor practice charges filed against the company by the Teamsters union .

The influential labor group represents UPS drivers and has been striving to organize Amazon drivers. However, it has faced challenges, primarily due to the company's reliance on thousands of third-party businesses that deliver millions of customer packages daily instead of employing drivers directly.

Currently, over 275,000 drivers are employed by these businesses , which are known as Delivery Service Partners, or DSPs.

The Teamsters and other labor advocates have long said Amazon exercises great control over the drivers - including by determining their routes, setting delivery targets and monitoring their performances - and should be classified as a joint employer.

Last year, the Teamsters announced they successfully organized a group of drivers who work for one delivery service provider (DSP) in Palmdale, California called Battle Tested Strategies. The labor union filed several unfair labor practice charges against Amazon after the company refused to negotiate a collective bargaining agreement with them.

On Thursday, NLRB spokesperson Kayla Blado announced that agency prosecutors had made “merit determinations” on three of these allegations, including one confirming that Amazon and Battle Tested Strategies were jointly responsible for the drivers employed by the firm.

Prosecutors also concluded that Amazon engaged in unlawful threats and withheld crucial information from the union. They further found that the two employers “unlawfully refused to negotiate with the union regarding the consequences of the decision to end” the DSP's contract last year, Blado said.

However, the prosecutors declined to pursue other allegations against Amazon, she said, including one accusing the company's termination of its contract with the unionized DSP as a retaliatory act.

If an agreement cannot be reached, the agency can file a formal complaint against Amazon, which would be adjudicated through the NLRB's internal legal process. Amazon retains the right to appeal a judge's ruling to the agency's board and potentially, to a federal court.

“Our position has always been clear: the Teamsters' allegations are baseless,” Amazon spokesperson Eileen Hards stated. “We anticipate that any remaining claims will also be dismissed by the agency if they choose to pursue legal action.”

Meanwhile, Teamsters leader Sean M. O'Brien voiced strong support for the findings.

“Amazon delivery drivers have taken matters into their own hands and secured a significant ruling that establishes Amazon's legal obligation to negotiate working conditions with its drivers,” O’Brien stated.