French President Emmanuel Macron on Thursday rammed a controversial pension reform through parliament without a vote, deploying a rarely used constitutional power that risks inflaming protests.

The move was an admission that his government lacked a majority in the National Assembly to pass the legislation to raise the retirement age from 62 to 64.

The Senate adopted the bill earlier on Thursday morning, but misgivings in the ruling party and reluctance by right-wing opposition MPs to side with Macron meant the government risked losing a vote in the lower house.

"We can't take the risk of seeing 175 hours of parliamentary debate come to nothing," Prime Minister Elizabeth Borne told MPs, shouting through the jeers and boos from the opposition benches who also loudly sang the French national anthem the Marseillaise in protest.

Trade unions and political analysts had warned beforehand that passing the legislation by decree, using the controversial article 49.3 of the constitution, risked radicalising opponents and would deprive the government of democratic legitimacy.

"It's a total failure for the government," far-right leader Marine Le Pen told reporters afterwards, adding that Borne should resign.

"From the beginning the government fooled itself into thinking it had a majority," she said.

Polls show that two thirds of French people oppose the reform and the government had insisted that it did not want to use article 49.3, which is viewed by critics as undemocratic.

"When a president has no majority in the country, no majority in the National Assembly, he must withdraw his bill," said Socialist Party chief Olivier Faure.

The government is set to face a confidence vote in the next 24 hours which could lead it to fall. Le Pen said her far-right party would file such a motion.

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