"The government's position is quite clear. Artworks will not be included in the assets liable for wealth taxation," Prime Minister Jean-Marc Ayrault told Europe 1 radio, after art world heavyweights sounded the alarm.
The French parliament's finance committee last week adopted an amendment, tabled by a member of the ruling Socialist Party, that would expand the assets covered by the ISF wealth tax to include art worth 50,000 euros or more.
Artworks have been exempted from the ISF since it was created in 1982.
The measure is now to go before the full assembly as it Tuesday starts examining the 2013 budget, which aims to save 36.9 billion euros ($48 billion), much of it through massive cuts in public spending.
Faced with an uproar from French art circles fearing a blow to the market, Culture Minister Aurelie Filippetti had voiced her strong opposition to the move, which even if voted in parliament needs government backing to become law.
But this was not enough to reassure the art world.
In a letter dated October 12, the heads of seven of France's top museums and cultural institutions wrote to Filipetti warning her the amendment was a threat to their prized collections.
Bruno Racine of the French National Library, Henri Loyrette of the Louvre, Catherine Pegard of the Chateau de Versailles, Alain Seban of the Pompidou Centre, Guy Cogeval of the Orsay Museum, Stephane Martin of the Quai Branly museum and Jean-Paul Cluzel of the Grand Palais) co-signed the letter.
"A new threat hangs over our duties, our ability to enrich our collections and to bring public and private artworks to the greatest number," they wrote.
"There are reasons to fear that taxing artworks will dissuade their owners from loaning them them, for fear they will be identified."
Taxing artworks, they warned, could also drive their owners to sell them abroad, leading to "the disappearance of historic collections, transmitted from generation to generation."
"The French public would be the first to suffer," they warned.
The row comes just ahead of Paris' FIAC contemporary art fair, which runs October 18-21.