The California State Teachers Retirement System, the second biggest U.S. public pension, will need to ask taxpayers for more money after investment losses left it underfunded by $42.6 billion.

The pension’s unfunded liability, the difference between assets and anticipated future costs, almost doubled from $22.5 billion in June 2008, according to a report Chief Executive Officer Jack Ehnes will deliver to the board Feb. 5. The fund will ask lawmakers next year for an increase of as much as 14 percent to what the state and school districts already pay toward employee retirement benefits, said the report, which was posted on the fund’s Web site today.