(AP Photo/Charlie Neibergall)

IOWA CITY, Iowa - A judge will soon decide whether to grant thousands of black employees and job applicants monetary damages for hiring practices throughout Iowa's state government they say have disadvantaged them for decades.

Experts say the case is the largest class-action lawsuit of its kind against an entire state government's civil service system.

The plaintiffs, up to 6,000 African-Americans passed over for state jobs and promotions dating back to 2003, do not say they faced overt racism or discriminatory hiring tests in Iowa, a state that is 91 per cent white. Instead, their lawyers argue that managers subconsciously favoured whites, leaving blacks at a disadvantage in decisions over who got interviewed, hired and promoted.

The case represents a growing front of discrimination litigation.

Anthony Greenwald, an expert on implicit bias who testified on behalf of the plaintiffs, said the decision would be one of the first of its kind because similar cases against corporations have usually been dismissed or settled before trial.

"The decision will be important. It will be certainly looked at outside of Iowa," he said.

Scholars and employment lawyers have shown a growing interest in implicit bias in the last several years, after Greenwald and other scientists developed the Implicit Association Test to test racial stereotypes.

Their research found an inherent preference for whites over blacks - in up to 80 per cent of test-takers and among many people who do not consider themselves racist.

The theory hit a legal obstacle last year when the U.S. Supreme Court disqualified a class-action lawsuit against Wal-Mart's pay and promotion practices for women. The court found the class was too broad and failed to challenge a specific hiring practice as discriminatory.

Lawyers defending Iowa have cited that decision in asking the judge to dismiss this case. But the high court's decision did not specifically reject the theory of implicit bias, and dissenting Justice Ruth Bader Ginsburg wrote that such claims can be allowed.

Class attorney Thomas Newkirk said the science and other evidence that shows disadvantaged groups such as blacks face employment discrimination in subtle ways "is becoming overwhelming."

"Clearly, the problem is not in Iowa alone, but we believe Iowa is the exactly the right place to ask society to take control of this important issue fairly for all races, and to seek a better future for all as a result," he said.

During a trial last fall, experts called by the plaintiffs' lawyers testified that blacks are hired at lower rates than whites with similar qualifications and receive less favourable evaluations and lower starting salaries.

Republican Gov. Terry Branstrad said last fall his administration had ensured agencies were following uniform rules to stop any abuse - but a top state employment official testified days later he'd seen no substantive changes to hiring practices in years. Blacks represented 2.9 per cent of the state's population in 2010 and 2.4 per cent of the state workforce.

Among those who testified was Charles Zanders, who was passed over for an interview for a position with the Iowa Communications Network in 2008 despite having worked 29 years in the telecommunications industry.

"I was very angry at that time and felt like I'd been stepped on," Zanders, 60, said.

In a brief submitted in December, plaintiffs' lawyers sought lost wages of about $67 million minus what they earned in the meantime.