What is the name of your state (only U.S. law)? New Jersey

I was verbally threatened (twice) on one of my contracted jobs recently. The person who made the threat said to me "I am going to take you out to the F-ing (using full word) parking lot and kick the Sh_t out of you". He made this threat twice...Immediately after his threat, he and his wife asked me to pack up and leave and not to finish my work. (His wife is the one who signed the contract engaging my services).

Is it illegal for someone to make such threats (I was told yesterday by a friend that it was illegal). Also, should I do anything to register this threat just to put in on the record. I'm not sure what my best course of action is. I still have to deal with these people regarding the work I was contracted to do and the money they owe me....and of course deal with their breach of contract...Thanks..