In an apparent bid to win back voters who have defected to the FN from his mainstream right Republicans, Sarkozy said that a vote for Marine Le Pen's movement was not "immoral" or "anti-republican" at an election rally on Tuesday night.
If it is "why has the republic allowed FN candidates to stand for 30 years", he asked.
Sarkozy went on to declare that "too much is too much" when it comes to immigration and that Syrian refugees should go home when the war is over.
It is not the first time that Sarkozy has taken a hard line on immigration and other questions dear to the FN's heart but, with his party desperate not to lose regions to the FN, he has clearly decided that a charm offensive will do the trick.
But that is embarrassing to the leaders of his party's slates in the two regions where President François Hollande's Socialists have withdrawn in their favour.
They have to persuade left-wing voters to come out and vote for them and their charm offensive is directed leftwards.
Xavier Bertrand, who is heading the Republicans in the crucial Nord-Pas-de-Calais-Picardie region, told his own party's leaders to "shut up" on Wednesday.
"I'm spending all my time commenting on one or other's statements," he said. "They should shut up! They only have to wait a few days so I have one thing to say to them 'If we can't lock you away, shut up!'."
Sarkozy's duty is to say that the behaviour of the FN leaders, notably Marine Le Pen, is immoral, he commented.
Le Pen, who heads her party's line-up in Nord-Pas-de-Calais-Picardie, mocked Sarkozy's efforts.
"He can always try [to steal FN votes]," she told Europe 1 radio. "He's tried 10 times and it worked once."
Jewish leaders in Marseille, the main city in the other region most likely to be won by the FN, Provence-Alpes-Côte-d'Azur, called on voters to turn out and vote for the Republican slate, led by Nice mayor Christian Estrosi, and praised the "tremendous sacrifice" of the Socialists, who will have no representatives at all on the regional council.
Estrosi on has promised to set up mechanisms to allow them to express their position and their local leader Christophe Castaner called on him to be a serious opposition to the FN if he does not win on Sunday.
In the eastern Alsace region, Jean-Pierre Masseret, who refused to withdraw the Socialist slate and has disowned by the national leadership, on Wednesday described himself as the candidate of "those people who don't lie down in front of diktats".