Former New York City Mayor Michael Bloomberg has pledged $1 million to back Washington state’s carbon fee ballot measure.

Initiative 1631 on the November ballot would charge large polluters an escalating fee on fossil-fuel emissions starting at $15 per metric ton.

Bloomberg announced his pledge Tuesday night in New York.

Opponents have raised more than $21 million, putting it on pace to break a fundraising record for statewide initiative campaigns. Top donors include several oil companies and the Koch Brothers.

Supporters have raised about $7 million.