37 CFR §1.1064

1. (a)Only one independent and distinct design may be claimed in a nonprovisional international design application.
2. (b)If the requirements under paragraph (a) of this section are not satisfied, the examiner shall in the notification of refusal or other Office action require the applicant in the reply to that action to elect one independent and distinct design for which prosecution on the merits shall be restricted. Such requirement will normally be made before any action on the merits but may be made at any time before the final action. Review of any such requirement is provided under §§ 1.143 and 1.144.