The opinion, Texas Ethics Opinion No. 585, is available here. It addresses what I know sometimes happens: a party does initial interviews with key firms in a city or state to preclude each firm from representing the opponent in major litigation. The Texas opinion concludes that a lawyer can't counsel a client to undertake that conduct if doing so has no other substantial purpose other than to delay litigation or burden the other party. Relying in part on an earlier Virginia opinion on the same subject, it said that whether Rule 4.04 (Texas's version of Model Rule 4.4) would be violated would be a fact intensive effort.