During a hearing Thursday, members of the California Air Resources Board will discuss cutting the number of battery-powered and hydrogen vehicles that automakers must produce for California and ten other states.

The rules, originally adopted in 1990, required that by 2003, ten percent of new cars sold in the state by the country's six major manufacturers be completely nonpolluting.

The rules have been modified four times since they were introduced.

The proposal to reduce the requirement for zero-emission vehicles is being criticized by environmentalists, health advocates and some leading political figures.