New rules have been passed in the San Francisco Bay Area that will require businesses to pay fees for the amount of carbon dioxide they emit.
The rules, due to come into effect on 1 July, could cost big emitters more than $50,000 (£25,000) a year, but most firms will pay less than $1 (50p).
Backers say the move sets an important precedent for the rest of the US.
But opponents say it may interfere with plans to introduce much tougher emissions targets across California.
The state's governor, Arnold Schwarzenegger, signed a landmark law designed to reduce greenhouse gas emissions and combat climate change in 2006.
The California Air Resources Board is due to release its preliminary proposals to implement the law next month, with a final plan to be approved later this year.
San Francisco's new fees, voted in by the Bay Area Air Quality Management District and said to be the first of their kind in the US, will cover more than 2,500 businesses in nine counties.
Companies will have to measure and report their own emissions before being charged 4.4 cents (2.2p) per ton of carbon dioxide they release.
The biggest payers will be a handful of power plants and oil refineries in the region.
The charges are expected to generate some $1.1m in their first year, which will help pay for programmes to measure and control local greenhouse gas emissions.
Many Bay Area firms have opposed the move, saying it may make it more difficult and expensive to do business in the region, the Associated Press reports.
Cathy Reheis-Boyd, chief operating officer for the Western States Petroleum Association, told the AP that a broader state-wide plan was needed to address climate change.
"We believe it's premature for local air districts to design local programmes before we have state programmes," she said.
The Bay Area is home to some seven million people and is among the wealthiest regions of the US.