What I learned when I lived in southern Connecticut is that if you were to cut the shrubs and if you did it incorrectly and the shrub was ruined/damaged, your neighbor would hold you responsible for the cost of the shrub...replacement cost for a mature shrub is expensive. Even if you cut the shrub correctly, your neighbor could claim you damaged the shrub and take action against you/your parents.
It would be best to talk to the neighbor first and let them know that you would like him or her to cut back the shrubs because they are encroaching into your space. Hopefully the neighbor will comply and peace between neighbors can exists.
If he/she does not comply, then do as
@plantladylin suggested and contact your local county/city about ordinances.
Another alternative is to talk directly to your neighbor's landscaper company...not the workers themselves, but the head of the company, and explain the situation. The boss can then give order to the workers to cut back the shrub to the property line. And it would be a good idea to clearly mark the property line so everyone can have a clear picture of exactly where the line is.
