The latest Ifop-Fiducial poll showed Ms Le Pen winning 23.5% in the first round on 23 April, one point ahead of centrist Emmanuel Macron.
The Paris prosecutor's office said Friday that investigating judges issued the request to lift Le Pen's immunity, and it was being transmitted by the French government to the European Parliament.
Contrasting it with Marine Le Pen's protectionist platform, they warned the far-right leader "would cause historic regression for the French, particularly the poorest".
French far-right presidential candidate Marine Le Pen said Friday U.S. President Donald Trump had apparently changed his mind on the U.S.'s role as the world's policeman, adding he may have been swayed by his administration.
"From the moment I implement intelligent protectionism that will fight against unfair worldwide competition, it will turn the economy around", Le Pen was quoted as saying, adding that growth will be accompanied by an increase in purchasing power.
The case was triggered by a complaint from the European parliament, which accuses the FN of defrauding it to the tune of about €340,000 (£290,000).
The request is unlikely to be approved by European lawmakers before the election.
"Undeniably he is in contradiction with the commitments he had made", Le Pen said.
Trump tells newspaper Obama aide might have broken the law
Rice has come under fire this week amid reports that she was responsible for the unmasking of the identities of Trump associates . She would not say whether she asked for names to be unmasked, or whether she sought intelligence reports on Trump's associates.
"It's totally normal procedure, I'm not surprised", Le Pen told France Info radio.
Ms Le Pen has, in turn, denied any links with racists, anti-Semities or xenophobes and is convinced she can appeal to moderate voters. The two-round presidential election is set for April 23 and May 7.
Le Pen argues that European Parliament investigators are singling her out because of her anti-EU views.
The Communist-backed Melenchon also wants a referendum on European Union membership after an attempt to renegotiate the European Union treaties.
His line - "When we workers are summoned by the police, we do go there, we don't have workers immunity" - left Le Pen silent and was widely picked up on social media.
Investors are growing more cautious about France and the euro ahead of an unpredictable presidential election in the eurozone's second-biggest economy. The company said Thursday it is taking action against those accounts and is removing sites with the highest traffic.
Melenchon's rise is also worrying French President François Hollande, a moderate Socialist who's so unpopular that he is not running for re-election.