Legal Question in Business Law in California

That is not legal duress. If you have a signed contract and the other party then says they will not pay for work done if you don't sign a new contract, your option is to sign or walk off the job and sue for breach of contract. You chose to sign, and now you are bound by the new contract. You may have other defenses to enforcement of the new contract, lack of consideration comes to mind (which does not mean rudeness; it means there was nothing given in your favor in return for modifying the contract in his favor). But just being told you won't be paid is not duress. Duress would be if they kidnapped your child and said they would kill them if you didn't sign, or they held a gun to your head. Just refusing to pay, when you could then just sue them, is not duress.

Mr. McCormick says what happened was not duress; I think there's some chance it might have been. The Restatement (2nd) of Contracts, a respected authority, says at pghs. 174 and 175, "A contract entered into under duress by physical compulsion is void. Also, if a party's manifestation of assent to a contract is induced by an improper threat by the other party that leaves him no reasonable alternative, the contract is voidable by the victim." It would be up to a judge to decide what actually happened to you in that "renegotiation" session and whether what the judge believes happened after hearing the testimony resulted in a void, voidable, or valid contract. Also, I'd suggest that you try to obtain a police report of the incident to see if it supports your possible civil case.