Italy's competition watchdog is investigating seven energy groups, including Enel, Eni and France's Engie, for allegedly illegally ramping up electricity and gas prices, it said Tuesday.

The suppliers, which account for around 80 percent of the market and include Hera, A2A, Edison and Acea, stand accused of making "unilateral illegal changes" to prices, the watchdog said.

More than 2.6 million consumers have "already suffered an unjustified price increase", the authority said in a statement, based on data provided by the companies.

The Italian government plans to spend more than 21 billion euros ($22 billion) on measures next year to ease the pressure of soaring utilities prices on households and businesses.

The authority accuses the companies involved of having modified electricity and gas tariffs without taking into account a decree issued on August 9 on measures to mitigate price hikes.

The companies must change the prices back to those in place before August 10, it said.

Marco Vignola, energy chief at the National Consumers' Union, hailed the "excellent news".

The investigation into the seven groups comes on top of a similar probe into energy suppliers Iren, Dolomiti Energia, E.ON and Iberdrola, the authority said.

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