Attorneys often write letters to third parties, in order to get something for their client. E.g. if A trespasses against B, B's attorney may write a letter to A stating that the trespass must be remedied, lest the matter end up in court. I will refer to the situation where an attorney implies that there may be legal action against a person as a "lawyer threat". The crucial thing about a lawyer threat is that it is simply an implication of possible legal action communicated to a third party, and it is distinct from to actually taking an action (filing a lawsuit, for instance). What, if any, are the enforceable limits on lawyer threats? By "enforceable", I mean that appropriate law boards in a state have the power to penalize (including officially reprimand) an attorney for violation of rules. I don't want to limit this to just formal demand letters (unless there's a rule against communication with third parties not via formal demand).
I presume that if a claim has legal merit, the attorney can represent to the third party that a lawsuit may arise if the situation is not remedied. My interest is the situation where this is not true, and I am specifically interested in established legal principles. ABA Model Rule 3.1 is related:
A lawyer shall not bring or defend a proceeding, or assert or controvert an issue therein, unless there is a basis in law and fact for doing so that is not frivolous, which includes a good faith argument for an extension, modification or reversal of existing law. A lawyer for the defendant in a criminal proceeding, or the respondent in a proceeding that could result in incarceration, may nevertheless so defend the proceeding as to require that every element of the case be established
Here is a hypothetical example. A sells widget X; B has some belief of a property interest in widget X (by patent, contract, or whatever); B's attorney "knows" that B's claimed interest is not going to succeed in court, because (if the basis is a contract) there is actually no contract between A and B. The attorney might run into legal problems if he files a meritless suit against A, but could sanctions be imposed for simply implying in a letter that the client may pursue a (meritless) lawsuit?
One part of the rule (which isn't clearly applicable to letters, anyhow) is where it says "includes a good faith argument for an extension, modification or reversal of existing law". This strikes me as a large escape clause allowing attorneys to contradict established law, if they think they can make a case for the contradiction.