(Reuters) -CalPERS, the biggest public pension plan in the United States, said on Monday it would vote against all Exxon Mobil ( XOM ) board members at its upcoming annual meeting on May 29, citing the oil major's legal action against activist investors.

Exxon, which is frequently the focus of critical shareholder resolutions, had filed a lawsuit earlier this year seeking to block a vote on a climate proposal submitted by two small activist investors, sidestepping the usual regulatory process to fend off similar measures.

And while the investors withdrew their resolution, Exxon continued the lawsuit, seeking legal costs and other relief.

CalPERS' decision comes days after proxy adviser Glass Lewis recommended investors vote against Exxon's lead independent director, Joseph Hooley, citing the same lawsuit.

CalPERS, which has about $490 billion in total assets under management and is a significant long-term owner of Exxon, said the lawsuit might have a "chilling effect on future shareowner proposals in the United States".