Legal Question in Business Law in California

No. The rule you speak of only applies to attorneys communicating with an opposing party that is represented by counsel.

No, but you must be somewhat careful how you go about it and what you say. If you are the opposing party you always have a basically unfettered right to communicate with your opponent, even an attorney has that right if they are the party rather than representing a client. However if you are not the opposing party you can face charges, no matter how unfair or unfounded, of witness tampering, threats or extortion, etc. So it's always best to go through a party's attorney unless you are the other party.

The rule is binding on lawyers and on non-lawyers who work for them. It applies only when the lawyer is representing someone else and not when she is acting on her own behalf. As Mr. McCormick notes, even where this rule doesn't apply, you could violate other rules and/or laws depending on the nature of your contact with the opposing party.