It is important to comply with the obligation to declare. If you do not declare, or do not declare correctly, your expose yourself to measures such as the temporary detention of the cash carried, and/or a penalty.
This could have a significant impact on your travel plans and the availability of the funds and cause great inconvenience. The legal basis authorizing the detention of undeclared or incorrectly declared cash is in article 4.2 of the Cash Control Regulation.
"where the obligation to declare cash is not fulfilled or incorrect, cash may be detained by an administrative decision in accordance with the conditions laid down under the national legislation".
According to Article 9 of the Cash Control Regulation, each EU country can introduce penalties for cases of failure to comply with the obligation to declare. Penalties applied by each country shall be prescribed in the national legislation.
The cash (part or the total amount) may be detained and a fine for non-declaration or other measures will be imposed subject to the conditions laid down in national legislation. These penalties have to be proportionate, effective and dissuasive and might entail the imposition of a significant fine.
We attract the attention to the fact that some EU countries have national provisions governing cash carried between EU Member States or even within one Country.
These are not an EU competence but we strongly recommend you to check what your obligations are before travelling.