According to Maersk, the reason behind the new special cargo misdeclaration fee is:

Globally, we experience around 20% of all cargo changing dimensions from booking to loading, and 6% causing issues due to misdeclaration where it is either not safe nor operationally feasible to handle the shipment. To make sure all cargo can be planned and handled safely we need to know the correct dimensions in advance.

What is more, the fee is not added as a penalty per se, but is introduced to cover all additional administrative effort these misdeclarations cause, amongst others the re-quote, terminal checks for feasibility and costs, as well as documentation amendments.

The fee is applicable to shipments which at gate-in exceed the booked dimensions in any way. Five days prior to departure date, our Special Cargo team will reach out to the customer to confirm the booked dimensions, as well as the End-Wall position in case the cargo is transported on a Flat-rack.

....as Maersk continued.

In case that the company doesn't receive updated dimensions before gate-in, but finds out that the actual dimensions exceed the booked dimensions, then the customer will receive a new quote with an updated rate and terminal handling charges, as well as the misdeclaration fee.

Maersk warned customers that is comparing dimensions between booked and actual dimensions, not the quoted dimensions. Consequently, even if the quote covers the exceeding dimensions, the misdeclaration fee will be applied, since the vessel was planned with the booked and not the quoted dimensions.