Civil rights groups on Thursday accused the U.S. Census Bureau of discrimination in its hiring of more than a million temporary workers to conduct the 2010 census, saying it ignored a warning from a federal agency that its hiring practices might violate the Civil Rights Act.

The Lawyers' Committee for Civil Rights Under Law, the Center for Constitutional Rights and the Public Citizen Litigation Group were among groups that sued the secretary of the U.S. Department of Commerce in April to end the hiring practices and obtain back pay for plaintiffs. They beefed up the lawsuit Thursday with new claims and plaintiffs.

The lawsuit, which seeks class action status in U.S. District Court in Manhattan, alleges the Census Bureau in hiring temporary workers over the past two years illegally screened out applicants with often decades-old arrest records for minor offenses or those who were arrested but never convicted. It accuses the bureau, a division of the Department of Commerce, of discriminating against more than 100,000 blacks, Latinos and Native Americans, who are more likely to have arrest records than whites.