Presidential candidate Kamala Harris’s latest bid for progressive hearts begins with a laudable ideal: Men and women should receive equal pay for equal work. Who can disagree, even without mentioning that discrimination by sex is illegal? The trouble is that the California Senator goes on to propose that political commissars oversee salary decisions for roughly 80 million American workers.

Ms. Harris’s plan, which she released this month, first cites tendentious statistics. “Women who work full time,” it says, “are paid just 80 cents, on average, for every dollar paid to men.” To repeat for the 862nd time, these figures are raw medians for all men and women, meaning they don’t control for occupational choices, career paths, hours worked, differing risks of on-the-job fatality, and so forth. The “80 cents” figure is simply incompatible with calls of equal pay for equal work.

Studies that compare apples with apples find a much narrower pay gap—or none at all. Last year two economists at Harvard examined data for Boston transit workers. In the aggregate, the women made 89 cents to the men’s dollar. But this gap, the paper says, “can be explained entirely by the fact that, while having the same choice sets in the workplace, women and men make different choices.” Women took more unpaid leave. Men logged more overtime.

This is not to claim that nobody in America’s vast labor market is ever treated unfairly. But as a means of countering whatever bad faith does exist, Ms. Harris’s plan would be a disaster. Instead of having workers claim and then prove discrimination, she wants the opposite: Companies would have to prove a negative—that they aren’t discriminating.

Under Ms. Harris’s plan, every business with 100 workers or more would have to get an “Equal Pay Certification” from the federal government. To earn this gold star, they must “prove they’re not paying women less than men for equal work.”