embargoes

Don't think so, you could only kill your own routes. You could do the extreme and kill all trade by leaving the UP.

Any reason for wanting to do so? I usually welcome the AI initiated trade routes.
Ok, thought about it more and realised what you were asking. You want to embargo one race and prevent other races from trading with it. It seems that trade embargoes were initially planned for the game but was taken out. We could see it returning as a feature in the future. Currently there is no way to do so short of war.
[Message Edited]

embargos are coming in the expansion.