The accusations came after the American president's controversial former eminence grise decamped to a palatial Parisian hotel days before the vote.
The elections for the European Parliament on May 26 in France will see President Emmanuel Macron's centrist party go head to head with Ms Le Pen’s National Rally, or RN, formerly known as the National Front.
Polls suggest that they are neck and neck with Mr Macron, Europe’s self-styled centrist champion, warning it would be a “catastrophe for France” should she finish ahead on Sunday. She has called for him to resign should he fail to do so.
Mr Bannon told Le Parisien this weekend he had opted to come to France as its election was "by far" the most important among EU member states. He predicted an “earthquake” next Sunday.
But his arrival sparked a barrage of criticism from the Macron camp, with his LREM party’s campaign director, Stephane Sejourne, remarking on Twitter: “Steve Bannon calmly parks his suitcases in Paris in his (hotel) Bristol suite at €2,500 (£2,200) per night to help Le Pen win!
“This is a breach of the sovereignty of the election…it makes you want to throw up.”
Pascal Canfin, LREM’s number two on the list for the polls, told Cnews that the RN was the "Trojan horse" for Mr Trump and Russian President Vladimir Putin in a bid to destroy the EU.
He said his party was calling on French TV channels organising the final election debates this week to set up "anti-fake news" unit that would counter false information live.
Mr Bannon has made no bones about wanting to unify European nationalist parties via his group, The Movement, and is known to be close to Miss Le Pen and Italian populist leader Matteo Salvini.
“If sovereignist, populist and nationalist movements do well in European elections, it will help these movements around the world and that will also be useful for Trump in America,” he told RMC.
But with a backlash against his presence gathering steam, he insisted that he was merely in Paris as “an observer”. Ms Le Pen, he told RMC, "doesn’t need my help to win. I’m her friend, her colleague perhaps but she will win this election by herself and it will be one of the greatest comebacks in the political history of her country".
Mr Macron trounced his far-Right rival in the 2017 presidential elections but she survived the aftermath and has been buoyed by the recent “yellow vest” revolt.
Ms Le Pen also waded into the row, insisting Mr Bannon played “no role in the campaign” but was in the French capital on business. A recent documentary showed Mr Bannon meeting with top RN officials who were apparently seeking help in stumping up party funding.
After a lacklustre start, the European election campaign is finally getting off the ground this week.
A TV debate among the top candidates was slated for Monday night while President Macron was due to give a lengthy interview to the regional French press on Monday.
While expected to stop short of making a direct call to vote for his party, aides said he would remind the French of the EU's contribution in areas such as social policy, the environment, security and fighting terror.
The French president, who has dramatised the election as a face-off between "nationalists and progressives", would also issue a warning against the imminent "deconstruction of the European project" should nationalists triumph.