A former Amazon.com Inc worker has sued the online retailer, saying it shorts as many as 21,000 warehouse workers nationwide on overtime pay.

The lawsuit contends that Amazon's practice of rounding start and end times for shifts to the nearest quarter hour costs workers up to 15 minutes of overtime pay daily, even when the company requires workers to put in the extra time.

Affected workers are engaged in activities that were not undertaken for their own convenience (and) necessary for the performance of their duties, the complaint said.

Amazon did not immediately return a call seeking a comment.

The lawsuit was filed on November 25 in federal court in Seattle, where Amazon is based, just ahead of the holiday shopping season. It seeks class-action status and the recovery of unpaid overtime plus interest.

In today's world of computers instead of punch clocks, there's no reason for rounding off in large increments, said Mark Thierman, a lawyer in Reno, Nevada. Millions of dollars of overtime may have gone unpaid, he said.

The plaintiff is Richard Austin, who worked for an Amazon distribution center in Fernley, Nevada, for about a year ending in August. Thierman's firm is one of four representing Austin.

According to U.S. Department of Labor policy, it is acceptable for companies to round start and end times to the nearest quarter hour as long as this does not result, over time, in a failure to compensate the employees properly for all the time they have actually worked.

Amazon shares rose $3.69, or 2.7 percent, to $142.19 in morning trading on the Nasdaq.

The case is Austin v. Amazon.com Inc, U.S. District Court, Western District of Washington, No. 09-01679.

(Reporting by Jonathan Stempel; editing by John Wallace)

Amazon Lawsuit