The White House said the pledge shows "the critical role that businesses must play in reducing the national gender pay gap."
The pledge was part of the first United State of Women Summit, hosted by the White House.
The 28 signatories include Pepsi, Amazon, Deloitte and Salesforce.
Each of the companies has agreed to undertake an organisation-wide analysis of their salary policies, to review hiring and promotion practices, and to include equal pay efforts in other equality initiatives.
A spokesperson for Pepsi said signing the pledge was part of the company's commitment to "end unconscious bias and create an inclusive environment where women are hired, developed professionally, and promoted into leadership positions."
More than two dozen companies have signed a pledge to address gender inequality in the workplace by regularly reviewing their own policies.