California Democrats have finally found a cause that’s worth suspending their environmental passions. The United Automobile Workers are struggling for a presence in Tesla’s Fremont plant, and organized labor has called in a political favor.

Since 2010 California has offered a $2,500 rebate to encourage consumers to buy electric vehicles. But last week, at unions’ behest, Democrats introduced an amendment to cap-and-trade spending legislation that would require participating manufacturers to get a sign-off from the state labor...