Both candidates will hold rallies just six days before the decisive second round.
France's powerful unions will also stage traditional May Day marches but the demonstrations will underscore the conspicuous absence of the united front they showed in 2002 when Le Pen's father Jean-Marie shocked the country by reaching the run-off.
On this day 15 years ago, some 1.3 million people took to the streets of France in union-led demonstrations to protest against the founder of the National Front (FN), including 400,000 in Paris.
This time, unions are divided over the choice between his 48-year-old daughter and 39-year-old Macron.
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Two, the CFDT and Unsa, have called for their members to back Macron yesterday.
But while three other more left-wing unions including the biggest, the CGT, have called for a demonstration against Marine Le Pen's vision of French identity and opposition to immigration, they have stopped short of backing Macron.
For many on the left, the former banker's outlook is too economically liberal.
Some militants have formed a movement they have called "Social Front" to block both candidates and will march today under a banner saying: "Rock and a hard place: Social Front, it will be won in the streets."
CGT leader Philippe Martinez said he "deeply disagreed" with that approach, arguing that Le Pen and Macron "are not the same thing".
"The National Front is a racist, xenophobic party that is anti-women and anti-workers because it is also an economically liberal party," he said.
"To see the CGT call on its members to vote for Macron, who is going to weaken the workers' lot... Is just astonishing," she said.
Macron is currently favourite to become France's youngest ever president, leading Le Pen by 19 points in the polls, but she has shown she is a canny campaigner.
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