Google has agreed to shell out $3.8 million to settle allegations that it underpaid women and unfairly passed over women and Asians for job opportunities, the US Department of Labour said on Monday.

The settlement includes $2.6 million in back pay to 5,500 employees and job candidates and requires Google to review hiring and salary practices.

Google also will set aside $1.25 million for pay adjustments for engineers over the next five years, according to the settlement. Any unused funds will be spent on diversity efforts at Google.

The allegations arose from a routine compliance audit several years ago required by Google's status as a supplier of technology to the US Federal Government.

The Office of Federal Contract Compliance Programs had found "preliminary indicators" that Google from 2014 to 2017 at times underpaid 2,783 women in its software engineering group.

Investigators also found hiring rate differences that disadvantaged women and Asian candidates during the year ended Aug. 31, 2017, for software engineering roles in the company.

The company already conducts annual pay audits, but like other big tech companies, it remains under public scrutiny for a workforce that does not reflect the country's makeup in terms of race and gender.

Google said it was pleased to have resolved the matter. "We believe everyone should be paid based upon the work they do, not who they are, and invest heavily to make our hiring and compensation processes fair and unbiased," the company said in a statement.