(Reuters) -Top mutual fund manager Vanguard Group on Thursday said it would roughly triple to 10 million the number of investors eligible to direct proxy votes in their funds, continuing an effort that would reduce the firm's direct impact on shareholder elections.

Closely-held Vanguard said it added four equity index funds to its "Investor Choice" program, bringing it to nearly $1 trillion in eligible assets from around $250 million previously. Vanguard has $10.1 trillion in total assets.

Participating investors do not specify votes at specific companies, but rather choose among several policy options including one that backs company recommendations and options that tend to support, or oppose, environmental and social matters in corporate elections.

Other fund firms including BlackRock and Charles Schwab's asset management arm have developed similar programs. At a time when the industry faces growing scrutiny of its influential votes, the programs could diminish the criticism facing the managers themselves.

Last year Vanguard's stewardship chief said only 2% of eligible investors opted in to a previous version of its voting-choice program, but vowed to keep building it.