Current client conflicts are addressed in the Code of Conduct, Rule 3.4-3:
A lawyer must not represent one client whose legal interests are directly adverse to the immediate legal interests of another client, even if the matters are unrelated, unless both clients consent.
This rule is known as the “bright line rule” recognized by the Supreme Court of Canada in R. v. Neil  3 SCR 631 and is based on a lawyer’s duty of loyalty to a client’s cause. As stated in commentary to Rule 3.4-3:
 The lawyer-client relationship may be irreparably damaged where the lawyer’s representation of one client is directly adverse to another client’s immediate interests. For example, one client may legitimately fear that the lawyer will not pursue the representation out of deference to the other client, and an existing client may legitimately feel betrayed by the lawyer’s representation of a client with adverse legal interests.
The application of the “bright line rule” means that a lawyer may not act both for and against the same client, even if the matters are unrelated and even if confidential information is not at risk. A conflict will exist if there is legal adversity between the two current clients. To determine if a current client or “bright line” conflict exists, you must assess the temporal relationship between the matters, the immediacy of the legal interests and the significance of the issue to the long-term interests of both clients. A client may also have reasonable expectations that his or her lawyer will never represent an adverse party. Such conflicts may, however, be cured by obtaining express consent from the clients.
Lawyers’ duties of candour and commitment can also be engaged when a lawyer seeks to act for an adverse party. The duty of candour to a current client means that the lawyer must disclose when accepting a retainer from an adverse party. The duty of commitment to the client’s cause means that a lawyer cannot drop an existing client to accept a retainer from a more lucrative or attractive client.
In the case of institutional clients who employ a number of law firms, consent to act against them may be implied, though this may only be applicable in rare cases. Client consent may be implied or inferred where you have a reasonable basis for believing that the client has consented, based on the terms of your retainer, the relationship with the client and the nature of the unrelated matters. Scarcity of legal services providers (due to degree of specialization or geography) may constitute a reasonable basis for believing that consent is implied.
Even if there is not legal adversity and the “bright line rule” does not apply, there may still be a substantial risk of a material or adverse effect on the lawyer’s representation of a client. In such a case, you must refer back to the definition of a conflict, set forth above.
Disqualification for Tactical Purposes
The Code of Conduct states that the “bright line rule” is not to be used for tactical purposes. Raising conflicts as a means to disqualify an opposing lawyer for improper purposes or to inconvenience the opposing party is not permitted. The CBA has prepared a helpful Conflicts of Interest toolkit including an article called “Avoiding Tactical Conflicts”. You will have to login on the CBA website to access this resource.
< 11.4 Types of Conflicts
11.6 Former Client Conflicts >