WASHINGTON – The Securities and Exchange Commission (SEC) on Wednesday approved a plan that would require companies to disclose how much more their chief executives are paid than their other employees, advancing an initiative that’s been years in the making.

The panel’s two Republican commissioners — Daniel Gallagher and Michael Piwowar — voted against the proposal, siding with business groups that cast the initiative as a costly burden that’s of little use to shareholders. The three Democrats, including SEC Chairman Mary Jo White, supported the proposal.

The mandate would require public companies to report chief executives’ total compensation, the median compensation of all other employees and the ratio between the two. Supporters say the disclosures will help shareholders make more informed decisions, and correct out-of-whack disparities in pay that have sparked public outrage.

Corporate lobbyists have launched a fierce battle to water down or scuttle the initiative. Multinational corporations said it would be tough to gather pay data for employees spread across several countries.

The rules, which could receive final approval later this year, would not apply to certain types of companies, including those with less than $1 billion in annual revenue or less than $75 million in securities held by the public.