Airdrop a couple thousand crates of cigarettes. Undermine the market. Lacing a few of them with opioids or strychnine might be a good idea too.
Heck, booby trap the cartons.
“Accidentally” leave a huuuge shipment or let one be directed to them, ALL laced with lethal doses of slow-acting poison.
I’ve advocated doing the same thing with poppy and MJ fields in their areas as well as food crops for two reasons: ‘salt the earth’ is a proven effective tactic back to the Romans and to send a message that to deal with these barbarians in ANY fashion is to risk your life even if we never get a bead on you for doing it. Buy their wheat and your city may be falling dead. Buy their cigarettes and you’ll fall over after lighting up.
It will make not only their goods toxic and unsaleable but also their very name. After enough deaths from tainted goods people will be self-motivated to keep them away for fear of their mere presence.
Yeah, some of that elephant tranquilizer street drug should do it!