Macron is now favourite to become France's youngest ever president, leading Le Pen by 19 points in the polls, but she has shown she is a cunning campaigner.
However, Le Pen's campaign manager, David Rachline, played down the accusations of plagiarism, saying the speech was a form of tribute to Fillon, which "was appreciated" by his supporters.
Yesterday Ms Le Pen said: "If there are waiting lists for the Alliance Francaise in Shanghai, Tokyo, or Mexico, for the French secondary school in Rabat or Rome. that is because France is something else, much more than the industrial, agricultural or military power that it must and can once more become".
Aides of French far-right presidential candidate Marine Le Pen on Tuesday brushed off criticism of her use of phrases lifted straight from a speech by conservative rival Francois Fillon in her May Day address to supporters. "Mr Macron adopted the slogan "France Together" it would have been more honest to say 'bankers together".
Said, a chauffeur who supports Mr Macron, said his father was targeted "because he was a foreigner, an Arab".
Mr Macron declared: "I will not forget anything and I will fight to the last second, not only against her project but against the idea she has of democracy and the nation".
Jean-Marie Le Pen co-founded the National Front party his daughter now leads. French flags were flying alongside European Union flags. "Go and convince (others), make her lose next Sunday", he told the crowd.
French presidential candidates trade barbs ahead of Sunday's crucial vote
As May Day marchers prowled and clashed on the streets of Paris.
The traditional May Day marches staged by France's powerful labour unions provided a useful gauge of the country's mood as it prepares to choose between Le Pen and centrist frontrunner Emmanuel Macron. The two face off Sunday in France's presidential runoff.
Cedric Villani, a high-profile mathematician and commentator wrote in the left-wing Liberation newspaper Tuesday that abstaining "is the equivalent of giving half of one's vote to Marine Le Pen in the most important election that France has had for several decades".
Ms Le Pen stood aside as leader of the Front National in a bid to woo a broader spectrum of potential voters.
Marchers included far-left candidate Jean-Luc Melenchon, who came in fourth in the first-round presidential vote.
But Ms Le Pen knows Mr Macron's time as economy minister in Francois Hollande's socialist government helps feed the narrative that he is the current President's lapdog.
Macron said he had received similar insults from the far-left and far-right for months, "but I'll look them straight in the eyes and say I don't have any lessons to learn from them".
Corporate Tax Reform: Expect the Unexpected
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