plaster on common re constructed wall

my neighbour extended common wall in 41/2 inch width from first floor up to 2 more floor, and 41/2 inch width are left from my side. but up to ground floor common wall is 9 inch width. my neighbour now wants to plaster on extended wall from my side, but because due to plaster my width are left 4 inch so i can not extended in future easly my neighbour house map are passed in MC office only one and half stories. what should i do denied or accept. give me legal right.