The NACE code is a coding system that identifies the field of activity of a business, and using a wrong code can cause the business to provide incorrect information on official documents such as tax returns. This can lead to the business being penalized by the tax office and even facing legal action. Additionally, using the wrong NACE code can cause the business to define its field of activity incorrectly, which can be misleading for other parties related to the business, such as customers, suppliers, or investors.