Board of director oversight of corporate political spending has expanded to 31 percent of the S&P 500, up from 23 percent in 2010. Companies that have more oversight mechanisms also spend about 30 percent more money on politics than those that do not, according to the report, which was commissioned by the Investor Responsibility Research Center Institute (IRRC) and conducted by the Sustainable Investments Institute (Si2), a non-profit, non-partisan research outfit for investors.

“We confirmed, by looking at a really big universe of companies, that boards of directors seem to be taking this issue seriously, and companies are responding to calls for more oversight and more transparency,” says Si2 executive director Heidi Welsh, who co-authored the study with Robin Young.