SACRAMENTO, Calif. (AP)_ Oil billionaires David and Charles Koch, prominent backers of the Tea Party movement, have spent one million dollars on the effort to suspend California’s global warming law.

They join two Texas-based companies, Valero Energy and Tesoro as contributors to the campaign for Proposition 23.

California’s global warming law, known as Assembly Bill 32, seeks to reduce greenhouse gas emissions statewide to 1990 levels over the next decade.

Prop. 23 seeks to suspend California’s 2006 law until the state’s unemployment rate falls below 5.5 percent for four consecutive quarters.

The initiative is opposed by environmental groups, Democratic lawmakers and Republican Governor Arnold Schwarzenegger.