73In that regard it must be noted that, according to settled case-law, action by Member States in areas that are not subject to harmonisation by EU law is not excluded from the scope of the provisions of the FEU Treaty on monitoring State aid. The Member States must thus refrain from adopting any tax measure liable to constitute State aid that is incompatible with the internal market (judgment of 5 December 2023, Luxembourg and Others v Commission, C‑451/21 P and C‑454/21 P, EU:C:2023:948, paragraph 104 and the case-law cited).
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