The commission said it was referring the matter to the European Court of Justice.
Ireland has only partially adhered to European laws on competition aimed at preventing companies from owning both transmission systems and the energy they carry, the commission said.
EU Energy Commissioner Gunther Oettinger said in a statement Thursday Ireland's delays in implementing European energy laws "have negative effects on all market participants and are therefore not acceptable."
An electricity regulation act passed by the Irish government in 2007 mandates the establishment of a "competitive" electricity market.
In January, the European Commission referred Ireland to the Court of Justice for failing to adhere to a mandate ensuring a 20 percent share of renewable energy by 2020.
On Feb .6, the Irish Environmental Protection Agency said the country was in violation of EU laws on pollution. It said nitrogen oxide emissions from the transportation sector were higher than mandated.