French Socialist leaders and other leftists accused Bernard Arnault, France's richest man, of lacking patriotism over his his decision to seek Belgian nationality.
Arnault, head of the LVMH luxury empire, confirmed the move a day before President Francois Hollande gave details of a 2013 budget that includes a 75 per cent supertax on top earners.
But he denied that becoming Belgian was a ploy to cut his future tax bill and cited personal and business reasons, saying he would continue to pay taxes in France.
The denial failed to blunt criticism at a time when Hollande is asking the French to bear tax rises and a freeze in public spending for the next two years.
"Get lost, you rich jerk!" said a front-page headline in the left-leaning Liberation daily, next to a picture of Arnault smiling in front of an overnight travel bag.
Arnault announced in a lawyer's statement he was suing Liberation for public insult over the headline, calling it vulgar and violent.
Leftist Jean-Luc Melenchon told RTL radio that France did not need such "parasites" and Socialist lawmaker Bruno Le Roux said Arnault was "betraying France's recovery".
"When you love France, you don't leave when the weather turns bad!" Harlem Desir, national secretary of the Socialist Party, wrote in a Twitter message.
Union leaders accused Arnault of profiting from French workers only to take his wealth across the border.
"It's immoral when you consider the situation of the workers on whose backs he makes his money," Francois Chereque, head of the CFDT labour union, France's largest, told France 3 TV.
"France, love it or leave it," read a headline on the front page of communist daily l'Humanite.
Arnault, ranked by Forbes magazine as the world's fourth richest man with a net worth of $41 billion, has argued that he does more than most for France's economy by heading a firm that contributes a hefty share of its international trade balance.
Taking the helm of LVMH in 1989, he turned the company into one of largest luxury groups in the world. His net worth exceeds the 30 billion euros France is looking to save in 2013.
His nationality move follows an appeal by Hollande to business leaders to lead by example in accepting tax rises.
Critics dismissed Arnault's argument that he was seeking French-Belgian dual citizenship for business reasons, saying he could work there as a Frenchman and already had several holding companies.
Leaving for Belgium could be a first step toward acquiring citizenship in Monaco, Liberation said. As a Frenchman in Monaco, Arnault would have to pay income tax. But he could avoid that if he drops his French nationality after becoming Belgian.
Hollande said on Sunday that Arnault "should have measured what he was doing".
Finance Minister Pierre Moscovici called the move a mistake.
"Chief executives must be exemplary," Moscovici told RMC radio. "Mr. Arnault has failed to set an example."
The case showed that tax conventions with countries such as Belgium, Luxembourg and Switzerland might have to be renegotiated in coming years, he said.
Hollande's 75 per cent tax on income above 1 million euros per year is the highest rate of any rich country.
Taxes often compel wealthy French to seek fiscal residence in neighbours with easier terms like Belgium, Switzerland and Luxembourg, at a cost of some 50 billion euros annually for the French state, according to a Senate report published in July.
Many converge in Brussels' fashionable Uccle district where Arnault has had a home since last November, according to the district's mayor. Armand De Decker.
"He did not mention taxes to me," De Decker told iTele television. "He has family in Belgium, he has major business partners and he told me that he wanted to invest more in business projects here."