But Susan R. Holmberg, a fellow with the Roosevelt Institute, a liberal public policy group, said that if the pay-ratio rule encourages employees to join unions, it is a good thing for workers, since it could lead to future wage gains.

“It magnifies the unequal pay practices,” Holmberg said. “It shows what a company’s priority is, and it triggers people’s sense of fairness.”

Mr. Trump “ran on this populist message,” she said, and it is odd that the administration would be taking another look at the pay-ratio rule, because "C.E.O. pay is the No. 1 populist issue.”

Investing in Human Capital

Still, there is some progress on the pay inequality front.

This year, the A.F.L.-C.I.O. Equity Index Fund and the New York State Common Retirement Fund reached an agreement with Regeneron Pharmaceuticals, a biotech company, to include new language on executive and employee compensation in its proxy statement. It says the company is taking a “non-elitist” approach by awarding stock options to all of its 5,500 employees, not just to executives. The change has helped lead the union and the New York pension system to withdraw a proposed shareholder amendment on the issue of pay.

Alexandra Bowie, a Regeneron spokeswoman, said the revised language in the company’s filings did not reflect a change in policy but a “broader effort to include more detailed and accessible language.”

As for Leonard S. Schleifer, the chief executive of Regeneron, his total compensation for 2016 was $28.2 million, almost 40 percent less than the year before, and nearly matching the 32 percent slide in the company’s share price.

Anne Sheehan, director of corporate governance at the California State Teachers’ Retirement System, said company boards need to be sensitive to issues of income inequality. “I have no problem with someone doing well, who creates value,” she said, “but I do think a company and a board as they look at compensation need to make sure everyone down the chain is also benefiting from the performance of the company.”

Boards need to consider not only how much top executives are getting paid, she said, but also whether rank-and-file workers are being compensated fairly too. The crucial question is this, Ms. Sheehan said: “Are they investing enough in the human capital in the company?”