Chipotle Mexican Grill Inc. shareholders approved a proxy-access proposal that was backed by activists, a rebuke to a board that has come under fire following a wide-ranging food-safety scandal.

Shareholders at Chipotle's annual meeting in Denver on Wednesday voted in favor of giving proxy access to shareholders holding 3 percent of the stock, a move that makes it easier for them to submit proposals. The investors voted down a company proposal that would have limited that access to a group of no more than 20 shareholders representing 5 percent of the company's stock.

Institutional Shareholder Services, a proxy advisory firm, and CtW Investment Group, which has union backing, had called for shareholders to vote for the proposal with the lower threshold, which ultimately won.