Help! My neighbour's taking the fence down!
Hi PWS. Tricky situation. Let's break it down.
First, if the chain link fence is on their property they are within their rights to take it down and replace it. The question is, how do they know it's on their property, and how do you know it's not? Do either of you have a survey that supports your position? Did a surveyor stake the property line out? That will clarify the situation.
If the chain link fence turns out to be on the boundary, or on your side of the line, then they cannot, technically, remove it without your consent. I say "technically" because practically speaking stopping a neighbour who is bent on finishing a project can be challenging. It's unlikely that the police or City will assist, so what are you going to do when they refuse to stop?
If you are sure (and have legal proof) that the fence was on your property then your best bet is to consult a lawyer and use the legal system to seek remedy. This probably isn't the immediate solution you are looking for, but it's the one that will likely give you the best outcome if, in fact, it can be proven that your neighbour acted improperly.