Amazon uses an automated system that tracks warehouse workers' productivity and can issue termination notices if they miss targets.

Amazon said it is "absolutely not true" that the software alone is responsible for firing workers, noting that managers may intervene in dismissals.

Union leaders are also expressing concern about how Amazon's move to cut delivery times from two days to one will affect workers.

Amazon, which has long faced criticism for how it manages workers, is now drawing scrutiny for how it fires them. A report by The Verge details the ecommerce giant's use of an automated system that tracks warehouse employees' productivity and issues termination notices if they consistently fall short of company goals.

Documents obtained by the technology news publisher cite an attorney for Amazon describing in a Sept. 4, 2018, letter to the National Labor Relations Board how Amazon fired "hundreds" of workers at one facility between August 2017 and September 2018 for failing to reach productivity targets and quality-control mandates. During that time, about 300 full-time workers were fired for inefficiency at the Baltimore site, representing roughly 10 percent of the fulfillment center's workforce, The Verge reported.

Part of a response to a complaint filed with the NLRB, the documents relayed how Amazon monitors worker productivity using a system that "automatically generates any warnings or terminations regarding quality or productivity without input from supervisors." Amazon's system also tracks "time off task," or what it refers to as TOT. If workers take breaks from scanning packages for too long, the system generates warnings that eventually can lead to firings.

Get Breaking News Delivered to Your Inbox

The report drew a rebuke Friday from the United Food and Commercial Workers International Union. "It's one thing for Jeff Bezos and Amazon to use a ruthless business model to destroy jobs for profit, but it is surreal to think that any company could fire their own workers without any human involvement," Marc Perrone, president of the UFCW, said in a statement.

Amazon denies that worker dismissals are handled through technology alone, saying that managers can intervene in the process.

"It is absolutely not true that employees are terminated through an automatic system," an Amazon spokesperson said in an email to CBS MoneyWatch. "Similar to many companies, we have performance expectations regardless of whether they are corporate or fulfillment center employees."

Prime suspect

Separately, Amazon's announcement Thursday that it would spend $800 million in the current quarter to cut delivery times for its top, or "prime," customers to one day instead of two drew fire from worker advocates.

"With two-day Prime shipping, Amazon fulfillment workers currently face speeds of 200 to 300 orders per hour in 12-hour shifts," longtime Amazon foe Stuart Appelbaum, president of the Retail, Wholesale and Department Store Union, said in a statement. "If Amazon plans to effectively double the speed, it must also address existing workforce needs and ensure its workers are safe."

Dave Clark, Amazon's senior vice president of worldwide operations, in an email called Appelbaum's concern "misguided and self-serving," saying the company's facilities are safe. Amazon is cutting its delivery times by improving its business processes and other innovation, "not by working harder," he said.