Country of Origin Labeling Amendment Act of 2003 - Amends the Agricultural Marketing Act of 1946 to revise country of origin labeling provisions, including: (1) specifying the model certification of origin program; (2) specifying producer protections; (3) reducing maximum retailer fines; (4) prohibiting treatment of country of origin violations as adulteration or misbranding; and (5) extending the implementing guideline deadline.