WASHINGTON – The Obama administration said Friday that it would require businesses with at least 100 employees to submit detailed pay data by gender, race and ethnicity in an effort to find firms that are “unlawfully shortchanging workers.”

A main focus of the new rules, which would take effect Sept. 30, 2017, was to advance efforts to ensure women are paid the same as men for doing the same job, as required by federal law.

The White House said that the median annual wage for a woman working full time was $39,600, 79 percent the median wage for a man.

Although the gap has “narrowed slightly” in the past two years, it is still too wide, the White House said.

“What kind of example does paying women less set for our sons and daughters?” President Obama said at a White House ceremony celebrating the seventh anniversary of his signing of the Lilly Ledbetter Fair Pay Act.

That measure made it easier for workers to challenge what they view as unfair pay.

The U.S. Chamber of Commerce called the reporting requirement too burdensome.

But Eleanor Smeal, president of the Feminist Majority Foundation, said the Obama administration’s action was “a big step forward.”

“An awful lot of times, people will say there is no income gap. There is, and we know there is,” she said.

Women’s rights activists have been pushing to gather such data since the late 1960s.

The federal action came after California last fall enacted a tough law to ensure that men and women who perform “substantially similar” work receive equal pay.

Friday’s move expands on a 2014 executive order that the Labor Department collect wage data by gender, race and ethnicity from federal contractors.

Under the new proposal, all employers with at least 100 workers would submit the data across 10 job categories and 12 pay ranges on a form they already are required to submit annually that includes employment data by gender, race and ethnicity.

Specific salaries would not have to be reported, and the data are not public.

The data would be analyzed to focus investigations into unlawful pay practices, the White House said.

Administration officials also hope that the data requirement will “encourage and facilitate greater voluntary compliance by employers with existing federal pay laws,” the White House said.

Randy Johnson, vice president of labor and employee benefits at the Chamber of Commerce, called the move a “fishing expedition to support a political agenda divorced from the facts.”