April 16 (Bloomberg) -- The California Public Employees' Retirement System, the largest U.S. public pension fund, said it will vote against the $19 billion purchase of Clear Channel Communications Inc., becoming the third big shareholder to oppose the takeover.

The acquisition ``is not in the shareowners' best interest,'' Calpers said on its Web site today. The fund owns 3.34 million shares of Clear Channel, or less than 1 percent of the largest U.S. radio broadcaster.

Calpers joins Fidelity Investments and Highfields Capital Management LP in opposing the buyout by private equity firms Thomas H. Lee Partners LP and Bain Capital LLC. The offer needs to be approved by two-thirds of shareholders at a special meeting on April 19 in San Antonio, where the company is based.

``It's certainly not surprising that institutional investors are lining up against this deal at the last minute,'' Fred Moran, an analyst with Stanford Group in Boca Raton, Florida, said in an interview. ``If the deal's not sweetened there's very little chance of getting the approval of shareholders.''

Moran has a ``hold'' rating on the stock and doesn't own it.

Shares of Clear Channel rose 11 cents to $36.35 at 4:01 p.m. in New York Stock Exchange composite trading. They have risen 2.3 percent this year.

Clear Channel declined to comment, said outside spokesman Timothy Lynch.

Highfields owns a 5 percent stake in Clear Channel, while Fidelity Investments is the company's largest shareholder with 9.7 percent.

To contact the reporter on this story: Don Jeffrey in New York at djeffrey1@bloomberg.net.

Last Updated: April 16, 2007 17:04 EDT