NEW YORK (CNN/Money) - Mutual fund rating firm Morningstar Inc. is running into some resistance in its efforts to provide a rating on fund managers' corporate governance practices, according to a published report Wednesday.

The service, which has traditionally rated returns and risk for more than 8,000 mutual funds, announced plans Aug. 24 to give grades of A through F for 500 of the larger funds' performance on issues such as regulatory issues, board quality and manager incentives.

It said at that time it expected to issue grades on another 1,500 funds in the coming months.

But the Financial Times reported that some major fund firms that are privately held have not turned over at least some of the information Morningstar is seeking. It reported Fidelity, Vanguard and American funds, the three largest fund companies, have all refused to supply details of manager compensation.

The paper said most of those funds got a B rating due to the lack of information.

Morningstar spokeswoman Kathy Habiger said the Financial Times story was misleading and incorrect.

She said Morningstar sent a survey to each fund company requesting information about manager compensation and ownership in the firm's funds, and that the overwhelming majority, both public and privately held, returned completed surveys.

CORRECTION The story that originally appeared Wednesday erroneously depicted the response Morningstar received from fund firms. CNN/Money regrets the error.

Habiger did not specifically address the cooperation of Fidelity, Vanguard or American funds in an e-mail she sent to CNN/Money.

The Financial Times report said many fund managers would not voice their opposition to the rating plan publicly but said privately that they did not believe it was possible to measure corporate governance with a single rating.

"Morningstar should stick to their knitting, which is measuring investment returns," the paper quoted fund consultant Geoff Bobroff as saying. "They do not have the expertise to judge companies' corporate governance."

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Morningstar argues that it has looked at corporate governance issues for years and is only now distilling that analysis into a simplified rating for investors.

"It's important to consider the intangibles associated with making an investment decision," said a statement in August from Kunal Kapoor, director of mutual fund analysis for Morningstar.

"Our analysts have long considered these less-tangible factors in an effort to help investors determine which fund companies do the best job of safeguarding their interests."