A particularly officious sounding goblin will point out that 'end worse for you guys than us' is, if not an outright threat, at least implies a threat, no matter how ludicrous the proposition is (this goblin is a dick). The feel that, having already petitioned the thieves directly and gotten no response, there's nothing the council can do for them.

And it's not extortion, it's payment for their protection services. Gosh.