He made his stark views known at a news conference after he met with Austrian president Alexander Van der Bellen.
He said: “Bump your views, do not try to qualify them, say the opposite and do not repeat their slogans. If you want to reduce populism you should not repeat the same message.”
Mr Junker’s warning comes as Marine Le Pen’s party Front National surges ahead in the polls.
She has successfully managed to drag the party’s reputation out of the hands of racists and anti-semites – who gave the Front National its far-right reputation in the 1970s.
However, this has prompted fears that the popularity of party’s like this will destabilise the EU and could even push it to the brink of an economic disaster if more countries leave the single currency.
Pierre Moscovici, the EU Commissioner for Economic and Financial Affairs, told The La Voz De Galica: “Mrs Le Pen aims to leave the euro and the EU.
“France leaving the single currency would be a tragedy for the euro zone and a catastrophe for the country, it would be the end of the European project created for French-German reconciliation.”
Mr Juncker has also expressed deep concerns over the pre-election climate in the Netherlands where Geert Wilders far right party, the Freedom Party is gaining popularity.
His team is set to keep a close eye on the outcome of the elections in the Netherlands as EU leaders believe Geert Wilders election could be disastrous.
Mr Wilders has caused a stir as he already has an advantage over his right-centre and centre-left rivals less than a month before the elections.
But the scandals in which he has been involved – including circulating false news about his rivals – only emboldens his supporters.
Mr Juncker has also expressed concern by the isolationist overtones of both the French and the Dutch campaigns which he says is similar to Brexit in the UK and the election of Donald Trump in the US.