In an ad released Friday, the former hedge fund manager's action group NextGen Climate called Charles and David Koch "chickens."
The 15-second ad buy features two little chicks walking around, clucking with the words, "We've been informed the Koch Brothers declined our invitation for a debate," in bold letters across the screen.
The ad will run during this Sunday's political talk shows in the Wichita, Kan., media market. Wichita is the home of the Koch brothers.
Friday's ad is a follow-up to one released by NextGen Climate earlier this month. It called out the Koch brothers for not responding to Steyer's invitation in April to debate U.S. energy policy.
NextGen also ramped up its campaign push on Thursday, noting that, while it might be a "drop in the big oil bucket" compared to what the Koch brothers may funnel into the 2014 cycle, Steyer is optimistic it will be effective in putting climate change on the political map.