According to Article 25 of the FuelEU Maritime Regulation, failing to comply with penalties can lead to serious repercussions, such as:

Expulsion from Ports: The ship may be expelled from ports, barring its entry and use of port facilities.
Flag Detentions: The ship may be detained by the flag state, preventing it from operating until compliance is achieved.
Restricted Access to Ports in Multiple Member States: The ship could face restricted access to ports in several Member States, significantly limiting its operational capabilities and access to essential services.

These measures highlight the critical importance of adhering to the FuelEU Maritime Regulation and ensuring timely payment of penalties to avoid significant operational disruptions.