The tech giants took a voluntary pledge last October to combat the spread of fake news, hoping to avoid more heavy-handed rules. Elections to the European parliament will be held in the 28 countries making up the European Union on May 23-26.
Foreign interference during the campaign and in national elections in Belgium, Denmark, Estonia, Finland, Greece, Poland, Portugal and Ukraine in the coming months has been a key concern for the Commission and EU governments.
Facebook, Google, and Twitter are still falling short, the EU executive said.
"More needs to be done to strengthen the integrity of their services, including advertising services," Commission digital chief Andrus Ansip, Justice Commissioner Vera Jourova, Security Commissioner Julian King and Digital Economy Commissioner Mariya Gabriel said in a joint statement.
"The data provided still lacks the level of detail necessary to allow for an independent and accurate assessment of how the platforms' policies have actually contributed to reducing the spread of disinformation in the EU," they said.