571.04 No person shall perform the specialized maintenance set out in Schedule II to this Subpart on an aeronautical product other than an aircraft operated under a special certificate of airworthiness in the owner-maintenance or amateur-built classification, except in accordance with (amended 2002/03/01; previous version)
(a) a maintenance policy manual (MPM) established by the holder of an approved maintenance organization (AMO) certificate issued pursuant to Section 573.02 with a rating of a category appropriate to the work to be performed;
From CAR 573
Entitlement to and Scope of Certificate
573.02 (1) The Minister shall issue to a maintenance organization that demonstrates that it meets the requirements of this Subpart an approved maintenance organization (AMO) certificate authorizing the maintenance of specified aeronautical products or the provision of specified maintenance services.
(2) The AMO certificate shall specify, in accordance with the criteria specified in section 573.02 of Standard 573 - Approved Maintenance Organizations, any category in which ratings have been issued and shall list the aeronautical products that the AMO is authorized to maintain or the maintenance services that the AMO is authorized to perform. (amended 2005/05/31; previous version)
(3) The scope of the work that may be performed under each rating specified on the AMO certificate is determined by limitations that are set out in the certificate.
From CAR Std 573.02
(3) A rating in the aircraft category will specify one or more types or groups of aircraft that are eligible to be maintained. Each type or group will be further subject to one of these limitations:
Any maintenance on the aircraft of the types specified, or any of their component parts, provided the maintenance is not specialized maintenance under the provisions of Schedule II of Subpart 571 of the CARs.