The most recent studies on the gender pay gap, which are not based on analogous work, show that women who work full time make 80 cents for every dollar paid to men, adding up to more than $400,000 in missed wages over the course of a woman’s career. The numbers are even worse for women who are also racial minorities — about $1 million in missed wages over a career for Latinas, Native American women and black women, according to an analysis by the National Women’s Law Center.

Under Ms. Harris’s proposal, companies that do not meet the pay certification standards would be fined 1 percent of their profits for every 1 percent difference in pay between men and women. The proposal also says that, should Congress fail to act, Ms. Harris would apply these standards to federal contractors unilaterally, barring companies that fail to obtain an “equal pay certification” from competing for federal contracts valued at more than $500,000.

“For too long, we’ve put the burden entirely on workers to hold corporations accountable for pay discrimination through costly lawsuits that are increasingly difficult to prove,” Ms. Harris’s campaign said in the announcement Monday. “We’ve let corporations hide their wage gaps, but forced women to stand up in court just to get the pay they’ve earned.”

Ms. Harris’s campaign has recalibrated in recent weeks, as the promise of a presidential bid that began with more than 20,000 people at a kickoff rally in Oakland, Calif., and strong first-quarter fund-raising totals has met a harsher reality, and is now polling in the single digits among Democratic voters. Ms. Harris recently began attacking President Trump more directly on the campaign trail, and has pitched herself as a merge of the unifying rhetoric of campaign rivals such as former Vice President Joseph R. Biden Jr., and the party’s more leftist wing, such as Senator Bernie Sanders of Vermont.

This week, Ms. Harris is set to campaign in central and western Iowa, where she is expected to highlight her economic message, particularly her plan to raise teacher pay.