My comunicé with the hotel:

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Initially, we would like to thank you for selecting to stay with us for your upcoming visit.
As of the 10th of December 2024, and in accordance with the new regulations announced by the Greek Government, changes
to the Climate Resilience Fee will be implemented as follows:

• For stays until the 31/Mar/2025, a Climate Resilience Fee of €4.00 per room per night will apply
• Stays from the 01/Apr/2025 until and including the 31/Oct/2025, a Climate Resilience Fee of €15.00 per room per night will apply

As such, your total daily room rate for your forthcoming stay will be adjusted accordingly.
We look forward to welcoming you to the Athenaeum Intercontinental Athens and we remain at your disposal for any further clarification or assistance you may require.

We would like to inform you that currently and until the end of June our hotel is under internal improvements aimed at enhancing your experience.We have taken all necessary measures to ensure your stay is comfortable and to continue offering our renowned hospitality
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I have a mix of paid and award bookings here so i guess it applies for all.
This fee is not some junk amenity fee as in the United States but seems genuine something from the Greek government,

in orginal Greek:
https://mcusercontent.com/a2a9e8bdd2...963;η.pdf

in English:
https://www.aade.gr/en/climate-crisi...ance-statement
https://www.aade.gr/sites/default/fi...kotitas_EN.pdf

https://news.gtp.gr/2025/01/07/clima...and%20response.
https://news.gtp.gr/2024/09/16/greec...-term-rentals/
https://skift.com/2024/01/10/greece-...esilience-tax/

Other hotels are also struck by it:
https://www.trypcorfudassia.com/new-...x-information/

It's a bit like Amsterdam's tourist tax, no way of avoiding it.
Even if one doesn't want to pay it,
i don't know if the competitors at Marriott & Hyatt's Greek hotels are willing to waving this tax on award bookings.
Others with experience might know.