California's governor, Arnold Schwarzenegger, has come out fighting for his green legacy, going on the attack against the oil companies and rightwing groups bankrolling a campaign to suspend AB32, a landmark environmental law.

Schwarzenegger, who is serving out his last weeks as governor, denounced a ballot initiative called proposition 23 that is seeking to roll back AB32 to reduce California's greenhouse gas emissions. He said it was a cynical move by Big Oil to protect its profits.

"Does anyone really believe that these companies, out of their black-oil hearts, are really spending millions and millions of dollars to protect jobs? It's not about jobs at all. It's about their ability to pollute and thus protect their profits," Schwarzenegger said in an appearance at the Commonwealth Club in Santa Clara.

He warned that the ballot initiative would cripple clean technology – the fastest growing sector of California's economy. It would delay the planned 2012 launch of a regional carbon trading market until California's unemployment rate drops below 5.5%, and remains there for a year.

Unemployment in California is 12%, and has fallen below 5.5% on only three occasions since 1970, so the measure is widely seen as a ruse to put an indefinite delay on action on climate change.

The intervention from the governor, and the release this week of the first television ads (below), mark a ramping up of the debate over California's landmark climate law.

The measure was the first of its kind in the US, in a state that stands out for its green efforts, from emissions standards on cars and power plants to a thriving 'clean technology' industry. A defeat would discourage other states from acting to reduce greenhouse gas emissions – especially now that Congress has dropped its climate change bill.

Two Texas-based oil refining companies, Valero Energy Corp and Tesoro Corp, have given about $4m and $1.5m to the campaign respectively. The billionaire Koch brothers, who own most of Koch Insdustries, and who reportedly have helped fund the Tea Party movement, contributed $1m through a Kansas-based subsidiary.

An obscure Missouri group, the Adam Smith Foundation, which reportedly ended 2009 with $109 profit, donated $498,000. There is no apparent relation to the Adam Smith organisation in the UK.

The group, which was established in 2007, has made small donations to local conservative groups in Missouri. A blog post on the foundation website said: "In this weak economy, we cannot afford stricter environmental regulations."

James Harris, a Republican political consultant in Missouri described as the guiding spirit of the organisation, told the Los Angeles Times: "California has some pretty crazy lawmakers who want to attack families' and individuals' opportunities to provide for themselves, and these are disastrous ideas. We want to make sure these types of ideas out west do not take hold."

The size of the funds flowing in from other states has attracted attention in California. "This is not at all routine," said Dan Newman, the executive director of Maplight, which works for greater transparency in political spending. "The level of spending is unusually high and it is also unusual in the fact that so much is from out-of-state."

It seems unlikely to stop. The president of the National Petrochemical and Refiners Association has appealed for even more support.

"I am pleading with each of you – for our nation's best interest and for your company's own self-interest," wrote Charles Drevna in an emailquoted in the Wall Street Journal.

A Los Angeles Times/University of Southern California poll this week suggested a tough fight over the ballot measure. It found 40% would support the ballot measure, and 38% oppose it. About a fifth of voters had yet to make up their minds.