The extremely unpopular pension reforms which raise the state pension age from 62 to 64, have been signed into law by French President Emmanuel Macron.
It took place hours after France’s highest constitutional council approved the modification.
The Constitutional Council rejected calls for a referendum from the opposition, but it also ruled that key portions of the amendments were invalid due to legal issues.
After the council made its decision, demonstrators set fire to Paris, and 112 people were detained.
Since January, there have been twelve days of protests opposing the reforms.
The measures will continue to be opposed, and on May 1st, unions are urging workers all over France to go to the streets once more.
President Macron argues the reforms are essential to prevent the pension system collapsing. In March, the government used a special constitutional power to force through the changes without a vote.
He signed the reforms into law in the early hours of Saturday morning.
The Labour Minister Olivier Dussopt has said he expects the reforms to come into effect by the start of September.
After the Friday ruling of the Constitutional Court, trade unions made an unsuccessful last-ditch appeal to the president not to sign the pension-age increase into law.
The unions pointed out that six concessions that had been added to the reforms were rejected by the court, so what was already unfair was now “even more unbalanced”.
Among the reforms struck down by the nine members of the Constitutional Council was a so-called “senior index” aimed at urging companies with more than 1,000 workers to take on employees over 55.
Mr Dussopt has vowed to improve the employment rates of those aged over 50 in an effort to ease concerns about the financial impacts of the raised retirement age.
The authorities had banned demonstrations in front of the Constitutional Council building in Paris until Saturday morning, but crowds of protesters had gathered nearby on Friday and the ruling was met with jeers.
Some demonstrators chanted they would continue protesting until the changes were withdrawn.
Later, several fires were set across the city as riot police tried to contain the situation, sometimes using tear gas. A Paris police official said 112 people have been arrested.
Fires were also lit during demonstrations in Rennes and Nantes, while there were tense standoffs at times between protesters and police in Lyon.