LOS ANGELES, July 9 (Reuters) - The state of Ohio on

Tuesday joined oil companies and business groups asking the U.S.

Supreme Court to reverse decisions that underpin California's

ambitious plans to regulate greenhouse gas emissions from cars

and trucks.

The Midwest state joined Valero's Diamond

Alternative Energy and other plaintiffs in challenging

Environmental Protection Agency (EPA) authority under the Clean

Air Act to grant waivers that allow California to set greenhouse

gas emissions limits that are stricter than the federal

government's, after a spate of Supreme Court rulings that weaken

U.S. agency authority.

"The Golden State is not the golden child. Yet in the Clean

Air Act, Congress elevated California above all the other States

by giving to the Golden State alone the power to pass certain

environmental laws," the Ohio plaintiffs wrote in their petition

to have the nation's top court hear its case.

Ohio's attorney general, who brought the case, and the EPA

did not immediately respond to requests for comment.