Calpers, the biggest U.S. public pension fund, said on Thursday it is seeking shareowner support for its proposal to require a majority vote to elect unopposed candidates to the board of Apple Inc.

The proposal is part of a broader push for majority-vote corporate board elections by Calpers, the $226 billion California Public Employees' Retirement System.

We believe a majority voting standard is necessary to provide shareowners better protection for the long-term -- accountability is our best protection in the face of uncertainty, Anne Simpson, head of corporate governance at Calpers, said in a statement.

At issue for Calpers, which is urging a nonbinding proposal, is the plurality vote rule at the iPad and iPhone maker.

Plurality voting is rapidly being replaced with majority voting in director elections, Simpson said. Approximately 80 percent of the S&P 500 and 60 percent of the Russell 1000 have adopted some form of majority voting -- an indication of the current direction of good corporate governance.

Calpers released its statement ahead of Apple's annual meeting later this month in Cupertino, California.

The fund noted that Apple is one of 58 U.S. companies it has asked to voluntarily adopt a majority vote rule.

(Reporting by Jim Christie; Editing by Robert MacMillan, Phil Berlowitz)