San Francisco,  A group of Google contractors have called out a recruitment agency over being underpaid for a long time, amounting to thousands of dollars in unpaid wages per affected worker, media reports said.

According to the workers, the payroll errors are happening so regularly that they believe it to be a kind of systematic wage theft, the Verge reported.

Guy Mylius, who was doing work for Google at Artech � a subcontractor hired via Google contractor Accenture, found he was underpaid four months into his job. At the behest of his co-workers, he checked his pay stub against the contractor's work order and found that he was contracted for 50 per cent more money than was making.

"I found out they had been paying me $20 an hour, but they were telling Google they were paying me $30.08 an hour," Mylius was quoted as saying. "That was in the middle of March, and basically they haven't done anything about it."

In his six-month term at Artech, the discrepancy added up to more than $10,000, the report said.

Several such workers discovered that their contractors were paying them less than it told Google they were earning.

While Accenture had set the pay rate for each role in a work order document before the hire was made, many found that the rate on their pay stub was $5 to $10 lower than the specified rate, the report said.

In most cases, workers were either completely unaware of the underpayment or believed it to be an isolated incident. It was only when they started comparing experiences that they realised how common the underpayment really was.

"We are looking into this matter," Accenture was quoted as saying, adding that it was investigating the claims to ensure all employees were properly paid.

"This seems to be a pattern," Mylius says. "It's not just that this was an error on my paycheck. I've personally talked to five or six people who are at Accenture who have had the same experience."

When the Verge reached Artech for comment, it said all employees were paid "in accordance with their employment agreements", per an internal investigation of the complaint. "Accordingly, at this time Artech denies the allegations in their entirety," Artech general counsel Eric Szoke was quoted as saying. "With respect to Artech's contractual terms with its client, that is a confidential matter between Artech and Accenture."

Shortly after Artech sent the statement, Mylius received his back pay in full from the company. No explanation was given for the timing of the repayment, the report said.