Paris (CNN) -- Far-right presidential candidate Marine Le Pen said Tuesday she is not endorsing either President Nicolas Sarkozy or front-running challenger Francois Hollande, both of whom are courting far-right voters on the immigration issue ahead of Sunday's runoff election.
"Sunday I will vote blank," Le Pen told supporters, "and in June (legislative elections), I will vote marine blue," a play on her name and the color of her party, the National Front.
In the first round of voting on April 22, Hollande received 28.6% of the vote, slightly ahead of Sarkozy's 27.2%. Le Pen received 18% of the vote -- enough to prompt both candidates to reach out to the National Front's 6.5 million voters.
"We have touched the soul and intelligence of the French people," Le Pen said Tuesday.
The National Front party -- founded and until last year led by her father, Jean-Marie Le Pen -- has "become the center of gravity of French politics," she said. Le Pen noted that Sarkozy and Hollande mocked the party at first, accusing its members of xenophobia, but now it is "the party that everybody wants to talk to."
She told supporters to vote "with your soul and your conscience."
Immigration has been a key election issue in France, alongside the struggling economy and high unemployment.
On Tuesday, in an interview on CNN affiliate BFM-TV and RMC Radio, Sarkozy, who leads the center-right UMP party, said he believes there are "too many immigrants in France."
"Our system of integration does not work, because before we had even integrated those we welcomed to our territories, others were arriving," the president said. "Having welcomed in too many people, we have crippled our system of integration."
Sarkozy has previously said he wanted to cut by half the number of foreigners allowed in the country over the next five years, saying he wants to welcome them in the right way, "with housing and employment."
He also said earlier that while immigrants should pass an exam on the French language and republican values, they should have rights and responsibilities equal to French citizens -- although that does not extend to the right to vote.
"I never called for closed France. I do not ask for zero immigration," he said Tuesday. "The truth is that when you invite more people than you can, you cannot integrate any more: not enough housing, not enough schools, not enough work."
However, in a speech Monday in Avignon, Sarkozy said, "We want to keep our landscapes, our values, our habits, the pride in being French. ... I never tell you to be afraid of the other, have the hatred of the other. ... I hate racism, homophobia, exclusion, violence, sectarianism."
Sarkozy also previously said that while he will hear the concerns of the National Front, he would not strike a deal with the far-right party.
The National Front has called for sharply curbing immigration, cutting numbers of asylum seekers and halting family unification policies for immigrants. On Tuesday, Le Pen said Hollande and Sarkozy have turned the country into "a train station and a question mark. ... The French left has unashamedly abandoned the little guys."
In a Tuesday speech, Sarkozy asked supporters, "If we deny France its identity, what will we have to share with other identities?"
"No one can forbid us from claiming our Christian roots," the president said. "... We have three days left to explain, persuade, lead -- for everyone to understand that on Sunday, he votes not for a candidate, but for himself."
He also spoke about the economy, saying, "Look what is happening in Greece, in Spain. ... We do not want that in France. Who wants that situation for French employees? Who wants that for the retired who have worked all their lives?"
Hollande, in a speech Tuesday, insisted that "the real issue of this election is unemployment."
Hollande, of the center-left Socialist party, had previously avoided questions about immigration. But last week, on a television show, he said there were "too many foreigners" in France, "but that does not mean that we must expel those who are here on our territory." Those who are in France illegally, however, should be deported, he said.
He repeated that stance Tuesday. "Foreigners who are here in the country legally should be able to stay there as long as they accept the principles of the republic," he said. "We cannot welcome foreigners when our economic situation does not allow it."
Sarkozy, he said, is trying to undermine Labour Day -- the first day of May, typically a holiday honoring workers' rights in France -- and its roots in unions. "Labour Day is Union Day," he said.
He also addressed unemployment, pledging to create jobs for youths, especially in high-unemployment areas.
If elected, Hollande would be France's first left-wing president since Francois Mitterrand left office in 1995. Sarkozy has been president since 2007.
Journalists Sarah Robertson and Rachel Ramsay contributed to this report.