US regulators accuse Google of underpaying female workers

"Every year, we do a comprehensive and robust analysis of pay across genders and we have found no gender pay gap," Google said in its statement.

Google and other technology companies have been trying to improve hiring practices that have historically doled out most of their technical jobs to white and Asian men. Their efforts to strike a better balance have been mostly unsuccessful so far.

For instance, only 19 per cent of Google's technology jobs are held by women. Overall, nearly one-third of Google's more than 70,000 workers are women.

The Labour Department's probe evolved from a lawsuit filed in January seeking to bar Google doing business with the federal government unless the company complied with an audit of its employee-compensation records. Google has said it has turned over some of the requested records, but withheld other information that it believes would invade its workers' privacy.

While Google and its peers have been disclosing embarrassing sexual and racial imbalances in their workforces for the past few years, the technology industry so far has kept its compensation practices a closely guarded secret.

The Labour Department is now scrutinising Silicon Valley for patterns of pay and hiring discrimination under its powers to vet companies that bid for lucrative government contracts.

Earlier this year, the Labour Department also sued Oracle, alleging that the business software maker routinely pays white male workers more than their female and non-white counterparts for comparable jobs.