Billionaire environmentalist Tom Steyer’s latest political fight is aimed at California’s high gasoline prices.

Steyer, who is known nationally for spending millions upon millions of dollars to get climate-friendly candidates elected to national office, is blaming oil company profits for the high costs.

He wants California’s legislature to mandate that oil refiners publicly disclose their profits from producing gasoline in the state, according to The Associated Press.

Steyer spoke about the proposal Wednesday in Santa Monica, Calif., with Consumer Watchdog.

“I am calling on the Legislature to address this problem,” Steyer said, according to the AP. “We have to protect Californians from these gigantic and unprecedented gas hikes.”

California’s average gas price was $3.70 a gallon Wednesday, compared with $2.63 nationally. It reached $4 a gallon in some areas last week due to supply disruptions.

A Consumer Watchdog analysis said refiners in the state tripled their margins between July 2014 and July 2015, to $1.61 a gallon.

“That is money that is being made off the pockets of Californians at the pump,” Steyer said.

A spokeswoman for Chevron Corp., which Steyer highlighted, told AP California’s high prices are due to a variety of factors, including a refinery fire, a strike, high state taxes and state fuel regulations.