The results demonstrate that shareholders are beginning to focus on executive pay and corporate boards are paying attention, Richard Trumka, president of the AFL-CIO, the largest U.S. labor group, said during a conference call to present the findings.

"The good news is that after 15 years, shareholders are beginning to protest," he said.

Compensation for top executives in 2010 had risen on average by 23 percent, the ALF-CIO said.

The union released the study two days after Citigroup shareholders shocked the giant bank's board with a vote on no confidence on its executive pay package for 2011, which included $14.8 million for Chief Executive Vikram Pandit. In an advisory "say on pay" vote required by the Dodd-Frank law, 55 percent of voting shareholders opposed the pay plan.

The surprise rejection vote was "a bell-ringer" showing how investors are giving companies tougher reviews, Trumka said. "Shareholders are more concerned, and hopefully that will have an even more moderating effect," he added.

The study by the AFL-CIO, a federation of 56 unions that represent more than 12 million workers, reviewed the pay for the chief executives of about 300 companies in the Standard & Poor's 500 index that so far had disclosed 2011 compensation in proxies filed with the U.S. Securities and Exchange Commission.

The results were generally consistent with surveys done by private-sector firms.

Total pay as reported in company "summary compensation tables" rose by 2 percent in 2011 compared with a 24 percent gain the prior year, according to a survey of about 225 companies in the Fortune 1000 that filed proxies by late March, Fran k Glassner, partner of Meridian Compensation Partners, said.

Compensation growth slowed amid the flat financial performance of many companies because boards of directors have added new measures to link executive pay more closely with actual results, Glassner said. "Pay for performance is starting to be engaged," he said.

Also, "say on pay" votes like the one at Citigroup, though only advisory, are adding public pressure for more corporate responsiveness, Glassner said.

The AFL-CIO study also analyzed how large mutual fund families vote on pay questions. As major shareholders, the firms often decide the outcome of proxy contests, yet rarely discuss their voting. As a result, the regulatory filings they make each summer provide a rare window on their thinking.

Among 40 fund firms last year, the median level of support for "say on pay" questions was 12 percent.

BlackRock, the world's largest money manager with about $3.7 trillion of assets under management, was dubbed a "pay enabler" by union officials. BlackRock voted against management on "say on pay" votes just 3 percent of the time last year, the study found.

Some smaller firms voted with management even more often, including Harbor Funds and the fund unit of Goldman Sachs Group. Both opposed only about 1 percent of "say on pay" questions.

Officials of BlackRock, Harbor and Goldman Sachs were not immediately available for comment.