Under § 7103(a)(14), COE "means personnel policies, practices, and matters, whether established by rule, regulation, or otherwise [e.g., by custom or practice], affecting working conditions, except that such term does not include policies, practices, and matters--(A) relating to political activities prohibited under subchapter III of chapter 73 of this title; (B) relating to the classification of any positions; or (C) to the extent such matters are specifically provided for by Federal statute[.]" (Emphasis added.) The fact that a statute deals with a matter doesn't mean that everything related to that matter isn't a condition of employment. In 55 FLRA No. 18, the Authority said the following: "The appropriate inquiry . . . is whether a statute at issue provides the Agency with the discretion to agree to the proposal." To the extent an agency has discretion in implementing the law, that discretion would be subject to bargaining.
The duty to bargain is limited to the mandatorily negotiable conditions of employment of bargaining unit employees. In FLRA's words: "[M]atters concerning conditions of employment are subject to collective bargaining when they are within the discretion of an agency and are not otherwise inconsistent with law or applicable rule or regulation." 53 FLRA 625, 648; 21 FLRA 61, 10-11. Unilateral changes in COE are unfair labor practices. For examples of what doesn't constitute a COE, see: 3 FLRA No. 8(appeal system for military appraisals), 7 FLRA No. 18 (hunting and fishing on military reservation), 8 FLRA No. 75, #1 (management access to investigatory files), 11 FLRA No. 99 (classification of positions), and 13 FLRA No. 73 (recycling discarded paper).