LISBON (Reuters) - Portugal's Constitutional Court has declared an extraordinary levy on renewable energy utilities illegal, backing a challenge from companies that have paid hundreds of millions of euros of the so-called CESE levy for years.

Renewable power sources such as dams, solar and wind parks supplied 61% of Portugal's electricity in 2023, one of the highest ratios in Europe.

The 2024 budget predicted the government would collect 125 million euros ($134 million) from the CESE across the entire energy sector, the same amount as last year.

The CESE was introduced in 2014, without including renewables, as part of Portugal's efforts to reduce the budget deficit after a debt crisis and international bailout. Despite being envisaged as a one-off, successive governments have kept the levy in force.

In 2019 it was expanded to tax renewable utilities' feed-in tariffs with a new objective - to ultimately reduce the electricity sector's accumulated tariff debt, which resulted from it previously applying regulated electricity prices to end customers that were lower than production costs.

In a ruling dated April 23 and released late on Tuesday, the Constitutional Court said the application of the CESE to renewable utilities "is unconstitutional as it violates the principle of equality".

It said that it cannot be concluded that the tariff debt was caused by renewable utilities, nor do they benefit directly from its reduction.

The normal CESE rate is equivalent to 0.85% of the value of regulated assets subject to the tax and is in addition to the income tax that utilities already pay.

Portugal's largest utility EDP, which has challenged the levy, chose not to pay 49.4 million euros in CESE tax for 2023, pending a court decision.

Since the CESE's introduction, the EDP Group has paid 558 million euros worth of the levy on its renewable and non-renewable assets, and its chief executive Miguel Stilwell de Andrade has criticised the tax as discouraging investment.

The CESE has also affected foreign utilities operating in Portugal, such as Spain's Iberdrola and Endesa.

($1 = 0.9304 euros)

(Reporting by Sergio Goncalves; Editing by Andrei Khalip and Mark Potter)

By Sergio Goncalves