All of the five large firms -- BlackRock Inc., Vanguard Group, Fidelity Investments, State Street Corp. and T. Rowe Price -- emphasize that executive pay should be linked to company financial performance. Their voting history, however, shows that they rarely use their ballots to challenge compensation packages for perceived underperformance.

Last year, the firms cast their advisory "say on pay" votes in support of senior executives 96 percent of the time or more at S&P 500 firms, according to research firm Proxy Insight.

That level of support was typical for recent years, as median pay among S&P 500 CEOs rose to $11.3 million in 2014 from $9.4 million in 2010, according to pay consultant Farient Advisors.

Big fund firms are facing more questions about their pay votes. BlackRock faces a shareholder proposal that calls for the world's largest asset manager to report on how it might bring its voting practices in line with its stated support of linking pay and performance. BlackRock calls such a report unnecessary.

BlackRock spokesman Ed Sweeney said the firm believes that talking privately with company officials is the best way to address pay issues. Last year, the firm engaged with about 700 U.S. companies and focused on executive compensation matters in 45 percent of those meetings, he said.

Vanguard spokeswoman Linda Wolohan said via email that executive pay "is a matter on which people have a wide variety of views (as supported by your survey results)." Pay is just one factor Vanguard considers in its proxy voting and it often addresses pay issues with company boards privately, she said.

Fidelity spokesman Charlie Keller said that its funds "are managed with one overriding goal: To provide the greatest possible return."

Spokespeople for T. Rowe Price and State Street declined to comment.

Publicly traded U.S. companies were required to submit the pay of their top executives for advisory votes by their investors under the 2010 Dodd-Frank financial reform act. With thousands of votes to cast each year through electronic platforms, the companies each have their own governance specialists to oversee their voting decisions.

Retired Massachusetts congressman Barney Frank, one of the act's creators, has suggested that funds with highly paid executives make poor overseers of CEO pay.