The gaffe-prone premier startled the French by saying the once untouchable 35-hour working week may be reconsidered as France battles to boost competitiveness and kickstart its struggling economy.
His comments came after Socialist President François Hollande, facing the heat from France's top companies over his economic policies, met the heads of global financial institutions in Paris to discuss the moribund global economy and ways to spur growth.
"Why not? There is no taboo," Ayrault said in a chat with readers of Le Parisien newspaper when asked if he would consider reverting to a 39-hour week. "I am not dogmatic."
"What worries me is that France is stalling and we need to restart the engine, full throttle," he said.
Some economic experts see a correlation between the rise in the French trade deficit and the 35-hour working week, which was first introduced in 2000.
According to the Eurostats agency, French hourly manufacturing costs are 20 percent higher than the eurozone average.
To add to France's woes, there is a €37-billion ($47 billion) hole in public finances, unemployment is past the three million mark at around 10 percent of the working population and there have been thousands of layoffs.
But just hours after the interview was published, Ayrault backpedalled.
"There is no question of going back on the 35 hours because it is not the cause of our economic difficulties," he told French radio.
"A reader of Le Parisien asked me this question. I said there were no taboo subjects," he said in a clumsy defence.
Ayrault's flipflop came after Labour Minister Michel Sapin said the current working hours should not be scrapped, although Finance Minister Pierre Moscovici has mooted a debate on the issue.
Leading trade unions also voiced their opposition to any measure touching the 35-hour week and some hinted at action if this were done.
The right-wing UMP party of Hollande's predecessor Nicolas Sarkozy, which had targeted scrapping the 35-hour week when it was in government, pounced on Ayrault's about-turn with glee.
"It's too good to be true! For some minutes I thought I was dreaming that the prime minister has finally assumed political courage," UMP leader Jean-François Copé told AFP.
"Alas, that only lasted a few minutes before he was immediately corrected... by his subordinate the labour minister," Copé said.
Some media outlets last week had hinted that a competitiveness report drafted by former Airbus chairman Louis Gallois would recommend scrapping the 35-hour working week, although this has been denied by his office.
Critics say the 35-hour week, pushed through under former socialist prime minister Lionel Jospin in 2000, is a major obstacle to any effort by France to improve its poor economic performance.
During his victorious presidential campaign earlier this year, Hollande vowed to protect the 35-hour week Sarkozy had tried to break apart.
The architect of the social experiment was former labour minister Martine Aubry, who was Hollande's main rival in the Socialist primary last year and was later snubbed as a possible prime minister.