In a major speech last week, the European Commission President proposed changes to the way the EU will operate after the UK leaves in March 2019.
But following the address, several member states hit back saying his reforms are not needed.
Responding this week, Mr Juncker labelled his critics ’ignorant’ and said most of what he proposed was already part of the 2007 Lisbon Treaty.
He said: “Reminding [heads of state] of the rules in the Treaty and creating surprise by doing so shows the state of ignorance of many of those who pretend they can lead Europe in all circumstances.”
In his annual State of the Union address last week, Mr Juncker laid out his future plans for the EU.
He told the European Parliament: “The wind is back in Europe’s sails. Now we have a window of opportunity, but it will not stay open for ever.
“We will keep moving on because Brexit isn’t everything, it is not the future of Europe.”
He added the British people would regret their ‘tragic’ decision to leave the bloc.
Mr Juncker expressed his desire to build a closer European Union based on a bigger euro zone and proposed a change in the way the EU made major decisions by removing the need for unanimity.
He argued for the creation of a fund to assist countries like Turkey and Albania with one day adopting the euro.
And he pitched the idea of merging two of EU’s top jobs – president of the European Commission and president of the European Council.
Mr Junker claimed this consolidation would allow the bloc to ‘function better’ and would be ‘easier to understand’ if there was ‘one captain steering the ship’.
But Eurosceptics responded critically to the speech, and are likely to view the move as a power grab by the Commission, which already has wide-ranging powers including proposing new legislation and managing the day-to-day running of the bloc.
Following the address in Strasbourg, MEP Nigel Farage said: “All I can say is, thank God we’re leaving.”
Beate Merk, a regional minister in Bavaria, said expanding the euro to the whole EU would be “a risky experiment that would greatly heighten Europe’s problems.”