MA general laws state something to the effect:
A homeowner has the right to trim any branches from a tree in the neighbors yard that are crossing his property line.
BUT as in a case that I was recently involved in, the trimming of said branches CANNOT directly cause the tree in the adjacent yard to die, if so, the homeowner trimming property line branches can be criminally AND civilly punished.
It's always best to look up the laws in your own area of operation. Just because it is so in one state, county or town, doesn't mean it holds true to your area...... Ignorance is no excuse for violating the law...