I ran into a similar issue with my federation. Every now and again, one of my members would get a bug up their butts and decide they wanted to declare war on someone. Then every single one of the other members would all vote 'yes' on this, leaving me to make the final call.

And it really put me in an annoying spot. Because if I voted 'yes' I'd be dragged into a decades long war that I had no stakes in, and to make matters worse, I'd wind up doing 90% of the work of winning it. But if I voted 'no' then all that would happen is that I'd get a -50 opinion penalty to whoever wanted to start the war, and then a a short time later they would put it to a vote again. If I said no a second time, my penalty increased to -100 and then a short time later, they'd call for a vote again. They'd keep doing this until I finally said yes.