Verdun's Socialist mayor Samuel Hazard cancelled Black M's concert on Friday, following an outcry by right-wing politicians and bloggers that led to him being "harassed by emails and calls of a racist nature", as he put it, citing a woman who told him "If it had been White M there would have been no problem."
The row blew up when a well-known far-right website, fdesouche.com, declared that Black M had "no place" at the commemoration of the 10-month battle in which some 300,000 French and German soldiers died.
French President François Hollande and German Chancellor Angela Merkel will attend the official ceremony.
The site cited words from tracks by Black M's former group, Sexion d'Assaut, to back the claim that he is "anti-France", including the phrase "country of qafirs [non-believers]" in the 2004 track Désolé and a reference to shooting up a school in 2014's Madame Payoshko.
It also accused him of being homophobic, referring to the phrase "I think it's high time that the queers perish" used by another group member in a 2010 rap - which led to the group making amends by working with LGBT organisations - and anti-Semitic because of a reference to "yids" in a cover of Doc Gyneco's Dans ma rue.
National Front demands cancellation
National Front leaders seized on the polemic and demanded that the concert by cancelled, accusing the government of "wanting to strip our history of all solemnity" and comparing the show to "spitting on a war memorial".
When right-wing paper Le Figaro published two articles on the row, the calls spread to the mainstream right, one MP, Valérie Boyer, starting a petition for the performance to be scrapped.
On Thursday the junior minister responsible for war veterans, Jean-Marc Todeschini, issued a denial that Black M's appearance was part of the official ceremony, although Hazard, a Socialist like Todeschini, said that it was the government that had put forward his name in the first place.
Finally, the grandson of a World War I soldier filed a legal case to prevent Black M appearing on the grounds that he was likely to insult the fallen and the state commemorations organisation turned down the council's request for 67,000 euros to fund the concert.
The pressure was too much for Verdun's mayor, who cancelled the show on Friday on the grounds that it was a danger to public order.
Grandson of World War II veteran
In the meantime Black M had hit back, saying he was a "child of the republic and proud to be" and pointing out that his own grandfather, Alpha Mamoudou Diallo, fought in World War II in an African regiment that was at Verdun.
The far right was exultant at the cancellation.
"At last the memory of our dead will be respected," declared party leader Marine Le Pen, while her deputy Florian Philippot claimed sole credit for the party, annoying fdesouche administrator Pierre Sautarel in the process.
But Hazard's Socialist comrades condemned it, Todeschini bemoaning an "outpouring of hatred ... in a country where freedom of expression and creation are fundamental values and rights", Culture Minister Audrey Azoulay denouncing a "nauseating moral order" and party first secretary Christophe Cambadélis slamming the "thought police" of the FN and its allies.
A former minister in the previous right-wing government joined them but added her own criticism of the Socialists.
Senegal-born Rama Yade, a member of the small Radical Party and wife of one of the centenary organisers Joseph Zinet, accused the government of "desertion".
"Once again it has caved in to the injunctions of the far right," she said in a statement.