Tech's biggest companies are joining the White House's pledge to close the gender wage gap.

The Obama administration launched its pledge in June, calling on companies to take steps toward equal pay for men and women. At the time, 28 companies signed the promise targeted toward private sector companies.

On Friday, 29 more companies joined them. Those companies included some of the biggest names in tech: Apple, Facebook, Dropbox, IBM, Intel, LinkedIn, MailChimp and Microsoft.

Airbnb, Amazon, Cisco, Expedia, Glassdoor, GoDaddy, Jet.com, Pinterest, Salesforce, Slack and Spotify signed the pledge in the first round.

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Those companies all agreed to conduct annual company-wide gender pay analyses across occupations, review hiring and promotion processes to reduce unconscious bias, and embed equal pay efforts into their broader equity initiatives.

"Equal work deserves equal pay," Apple said in a statement accompanying its signature. "This past year, Apple looked at the total compensation for US employees and closed the gaps we found."

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In its statement, Facebook said it values diversity.

"At Facebook we value those who bring varying perspectives, for many reasons including background, community, culture, race, ethnicity - and gender. We call this cognitive diversity, and we want more of it. It propels our mission: to give people the power to share and make the world more open and connected," Facebook said.

Other companies highlighted the work they are already doing to reach pay equity, and emphasized their commitment to the cause.

IBM quoted its founder, Thomas J. Watson Sr., who said in 1935, "Men and women will do the same kind of work for equal pay. They will have the same treatment, the same responsibilities and the same opportunities for advancement."

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Women working full-time today earn 79 percent of what men earn. For black women, that number is 63 percent. For Latinas, it's 54 percent.

The pay gap is smaller in tech than in other industries, but it's still there. According to a 2015 study from the salary monitoring site PayScale, the pay gap in tech is 1.4 percent. At the executive level, however, the pay gap is larger in tech than in other industries.

The White House announced the new signatories Friday in honor of Women's Equality Day.

TopicsAppleFacebookBarack Obama