The UK is expected to face one case over Scottish Power's contract for use of the interconnector between Northern Ireland and Britain, signed before an EU directive came into force.
But the main thrust of today's package of measures will be directed against countries such as France, Germany, Italy and Spain, for failing to implement EU laws designed to liberalise the bloc's energy policy.
The precise list of countries to be hit with formal proceedings will be decided at a meeting of the commission in Strasbourg.
With only five of the 25 nations certain to escape unscathed, and several nations likely to face a clutch of cases, today's decision will be unprecedented in scope. Only Cyprus, Malta, the Netherlands, Denmark and Slovenia are likely to avoid censure. The British case is seen as largely a technicality since the contract concerned is due to expire shortly.
EU countries will be targeted for failing to write into national law measures to force "unbundling", which would allow competitors to move into operations controlled by former state monopolies.
The commission is also due to take action against a French decree restricting foreign ownership in 11 "strategic sectors" ranging from dual-use civilian-military technologies to casinos.
France will have two months to explain how the decree, the centrepiece of its "economic patriotism" policy, can be reconciled with EU rules on the free movement of capital. The action in the energy market is a prelude to battles between the commission and EU nations accused of obstructing the internal market.Reuse content