Is this a violation of Rules of Conduct?

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

I have an attorney. My attorney sent a formal letter to the opposing side's attorney and also spoke with him by telephone informing him that I have retained [my attorney] as counsel of record. The opposing counsel has twice sent me a letter directly and not to my counsel of record. Is that permitted or would that be considered a violation of Rules of Professional Conduct? Could I file harassment charges against the opposing counsel for his two threatening letters sent to me directly instead of through my attorney?

Are we to assume from the meagerness of information that your attorney is representing you as “counsel of record” in a pending a civil lawsuit? If so, he wouldn’t be so advising this other lawyer whom you identify as “opposing counsel” of that fact by a letter.

He would have signed and filed a pleading or motion on your behalf or signed and filed a notice of appearance as counsel of record on your behalf and copied the “opposing counsel”. Otherwise he would not be your “counsel of record”.

From that point on it would not be proper for “opposing counsel” to be communicating with you outside of the courtroom without your attorney’s consent.

Nor would it be proper for the attorney to directly communicate with you on subject matter upon learning that you have retained an attorney to represent your interests in the same subject matter without your attorney’s consent.

I don’t’ know what your objective is here, but I think you are making a fuss over nothing of great consequence. Anyway, your attorney should be the one to be most offended so let him deal with it.