San Francisco, May 11 (IANS): Despite criticism and work pressure complaints from its warehouse employees, e-commerce giant Amazon has quietly begun rolling out its one-day Prime shipping, cutting down from the traditional two-day delivery window.

"We have been able to confirm the new option showing up on various Prime items with a new 'Prime Free One-Day' label replacing the usual two-day promise," The Verge reported on Thursday.

Details about the exact regions where the functionality has started rolling out remains unclear as of now.

In an earnings call earlier in April, Brian Olsavsky, Chief Financial Officer (CFO) at Amazon, announced the company's plan of investing $800 million and building most of this one-day Prime delivery capacity throughout 2019.

However, Stuart Appelbaum, President of Retail, Wholesale and Department Store Union at Amazon has expressed his fear that speeding up deliveries could be dangerous for employees at the Amazon fulfilment centres.

Appelbaum, said workers were already struggling to keep pace and handle 200 to 300 orders during a single 12-hour shift, the media had reported.

The multi-billion dollar company already offers a selection of items that are eligible for free one-day shipping and it rolled out two-hour delivery in certain cities with its Prime Now service.