The letter from Titan CEO Maurice Taylor to French Industrial Renewal Minister Arnaud Montebourg was in response to a request for Titan to consider investing in a loss-making Goodyear plant in Amiens, northern France.
"I have visited that factory a couple of times. The French workforce gets paid high wages but only works three hours," Taylor said in the letter, dated February 8 and obtained by French business daily Les Echos.
"They get one hour for breaks and lunch, talk for three and work for three. I told this to the French union workers to their faces. They told me that's the French way!"
Goodyear said last month it was set to close the plant, which employs 1,173 workers, following five years of failed talks with unions.
Taylor said Titan had a long history of buying and turning around troubled factories but in this case was not in any way interested.
"Sir, your letter states that you want Titan to start a discussion. How stupid do you think we are? Titan is the one with the money and the talent to produce tyres. What does the crazy union have? It has the French government," Taylor wrote.
He said France's industrial base was under threat from low productivity and cheap imports, including tyres from China that he said were made in subsidised factories.
"Titan is going to buy a Chinese tyre company or an Indian one, pay less than one euro per hour wage and ship all the tyres France needs. You can keep the so-called workers. Titan has no interest in the Amien North factory," he wrote.
But Goodyear's 'crazy' union as Taylor described it hit back on Wednesday slamming the letter as 'insulting'.
"Titan is struggling to break into the European market and it's not with words like this that they are going to achieve it," the factory's CGT union chief Michael Wamen told Europe1 radio.
"It shows that this CEO, of a multinational company, is more suited to being in a psychiatric hospital than leading a company like this."
Montebourg, a normally outspoken minister has so far declined to comment, saying he does not want to harm the interests of France.
His stance marks a different tone to that which he took towards steel giant Lakshmi Mittal, when the British based tycoon threatened to close his plant in Florange, eastern France.
An outraged Montebourg said Mittal was "no longer welcome in France" and could take his business elsewhere. Mittal responded by calling Montebourg 'irrational'.
France's Socialist government is struggling to boost the productivity of its industries in the face of increasing global competition. French firms have announced thousands of job cuts in recent months as the economy stagnates.