An oath by a solicitor or other employee in a law firm not to disclose any information in regards to a previous client otherwise placing that lawyer or employee in a conflict of interest with other clients of the same law firm.
In referring to US law, Justice Sopinka of Canada's Supreme Court, in MacDonald Estate v Martin (1990) 3 SCR 1235 stated:
"Once it is established that there is a substantial relationship between the matter out of which the confidential information is said to arise and the matter at hand, there is an irrebuttable presumption that the attorney received relevant information. If the attorney practises in a firm, there is a presumption that lawyers who work together share each other's confidences. Knowledge of confidential matters is therefore imputed to other members of the firm. This latter presumption can, however, in some circumstances, be rebutted. The usual methods used to rebut the presumption are the setting up of a Chinese Wall or a cone of silence at the time that the possibility of the unauthorized communication of confidential information arises. A Chinese Wall involves effective screening to prevent communication between the tainted lawyer and other members of the firm. A cone of silence is achieved by means of a solemn undertaking not to disclose by the tainted solicitor."