Tech companies have been under pressure for years to disclose their employment data, dating back to 2010, when the San Jose Mercury News filed a Freedom of Information Act request to get the statistics from the Equal Employment Opportunity Commission.

Companies must file a form called an EEO-1, detailing their ethnic and gender breakdowns. Companies such as Google, Apple Inc. and Yahoo Inc. fought the disclosures and won, persuading the EEOC to withhold them. But earlier this year, amid public demands by Mr. Jackson and Oakland, California-based, things changed.

The best-known tactic in the campaign was against Twitter, which has a higher rate of African-American and Latino users — estimated at about 41 percent — than other social media platforms. They threatened to mount a campaign on Twitter to force the disclosure. Twitter declined to comment beyond its blog post, releasing the data.

Mr. Jackson said Rainbow Push has had a Silicon Valley office for 15 years and that it's just using the same economic weapons that civil rights activists have used since the 1960s. "We leveraged our buying dollars to build reciprocal relationships," he said. "We've always had two weapons: our dollar and our vote."

Disclosure is only a start, but it's significant, nonetheless.

“I've seen a lot of (diversity) initiatives, but I've seen very little change in the big picture. It's a good start,” said Amanda Kimball, a researcher at the University of California-Davis Graduate School of Management who tracks the female leadership of Silicon Valley companies in an annual study.