By Jessica Wohl

May 23 (Reuters) - CalPERS, the biggest U.S. public pension fund, said on Wednesday it plans to vote against nine Wal-Mart Stores Inc board members amid allegations that the retailer's top brass failed to adequately investigate widespread bribery in Mexico.

The California Public Employees' Retirement System is the latest shareholder to publicly voice concerns over the board's role after the New York Times reported in April that Wal-Mart de Mexico, which is majority-owned by Wal-Mart, used illegal payments to win market leadership in that country and that top Wal-Mart executives knew about the matter and tried to cover it up.

The alleged bribery scandal has prompted several high-profile Wal-Mart investors to publicly vent their displeasure with key board members including Chief Executive Mike Duke and former CEO Lee Scott. Still, such actions likely will be only symbolic since the family of Wal-Mart founder Sam Walton controls roughly half of the company's shares.

CalPERS said it plans to vote its 7.77 million Wal-Mart shares against Duke, Scott, Chairman Robson Walton and six others.

CalPERS said it believes the nine were in positions of authority, oversight or management of the company's operations during the period when the alleged bribery took place.

The other six are James Breyer, Michele Burns, Douglas Daft, Jim Walton, Christopher Williams and Linda Wolf. Wal-Mart has 16 nominees in the June 1 election.

The announcement from CalPERS comes a day after CalSTRS, the California State Teachers' Retirement System and the second-largest U.S. public pension fund, said it planned to use its 5.3 million Wal-Mart shares to vote against the re-election of the entire board at the company's annual meeting on June 1.

CalPERS said it would also vote for two of three shareholder proposals up for a vote. It plans to vote for a proposal regarding the reporting of political contributions and another proposal related to creating an incentive compensation report.

Wal-Mart has said it recommends shareholders vote for the entire slate of 16 board nominees and against all three shareholder proposals.

Shares of Wal-Mart continued to rise on Wednesday, and were up 0.64 percent at $64.14 in afternoon trading. The shares are trading at their highest levels since April 2000 amid economic concerns, which often lead investors to look for safe haven stocks.