After serving up 38 million ads from a group supporting the legalization of marijuana since August 7, Facebook told the group on August 16 that it could no longer use a pot leaf in its ad, since it might promote smoking.

“The image in question was no longer acceptable for use in Facebook ads,” wrote Facebook spokesman Andrew Noyes in an e-mail to Wired.com. “The image of a marijuana leaf is classified with all smoking products and therefore is not acceptable under our policies.”

But the Just Say Now campaign contests that Facebook isn’t harshing on their mellow — it’s censoring them, especially given that marijuana legalization is on the ballot in the upcoming election in California. And it’s calling on its supporters — some 6,000 fans on its Facebook page — to swap out their profile picture for an image of a pot leaf with a banned box over it.

“We aren’t trying to sell people pot. This is a policy issue,” Hamsher told Wired.com, noting that more than 50 percent of inmates in the federal prison system were there on drug charges and that law-and-order types like former Reagan administration lawyer Bruce Fein support decriminalization. “The time is right for this and Facebook shutting this down is a real blow when we are trying to open up a conversation…”

“It seems like a decision made to appease somebody’s grandma,” Hamsher said.

Or a decision made to appease some nanny investor.