In the year since State Street’s “Fearless Girl” statue started her showdown with Wall Street’s “Charging Bull,” the $2.6 trillion asset manager has faced a confrontation of its own in corporate boardrooms: pressing firms to add more women to their boards.

More than 150 companies State Street targeted for not having a female director as part of its Fearless Girl campaign have added at least one, it said Wednesday.

The company sent letters and engaged in an unprecedented withholding of votes from directors responsible for nominating their colleagues at more than 400 companies.

“We still have a long way to go but we’re happy to see the impact we’ve had so far,” said Rakhi Kumar, who leads environmental, social and governance investment strategy at Boston-based State Street.

“This is about diversity of thought and backgrounds. Women could be 50 percent of your customer base, and 30 percent of your employees. How are you representing the views of half of society?”

Investor-led efforts to get women on boards are at their strongest in years. In recent months, the California State Teachers’ Retirement System said it will withhold votes from directors at companies without women on their boards.

BlackRock Inc. has said it now expects companies to have at least two women on their boards and proxy adviser Glass Lewis & Co. in December pledged to start recommending votes against directors at Russell 3000 Index companies with all male boards in 2019.

The number of companies in the Russell 1000 Index without any women on their boards has fallen to 47 from a recent high of 176 in 2009.

State Street has added boards in Japan and Canada to the target list this year, Kumar said.