Police fired tear gas at protesters on the Place de la Concorde in Paris, where some 7,000 people demonstrated against the government's pension changes in a spontaneous and unplanned rally.
A Reuters reporter saw cobble stones being thrown at the police, who charged to break up groups of protesters.
The demonstration was across the river Seine from parliament, where Prime Minister Elisabeth Borne earlier on Thursday announced her government would push through the reform using a special constitution clause, as her minority government could not get the necessary backing from the opposition conservative Les Republicains party.
President Emmanuel Macron shunned parliament and opted to push through the highly unpopular Bill. The bill will raise the retirement age from 62 to 64 by triggering a special constitutional power.
The risky move is expected to trigger a quick no-confidence motion in his government.
The decision was made a few minutes before the vote was scheduled, because the government had no guarantee that the Bill would command a majority at the National Assembly, France’s lower house of parliament.
The Bill is the flagship legislation of Mr Macron’s second term, but it has prompted major strikes and protests across the country since January.
As legislators gathered in the National Assembly on Thursday to vote on the Bill, the leftist members of the parliament started singing the Marseillaise, the French national anthem, preventing Prime Minister Borne from speaking and prompting the speaker to suspend the session.
The atmosphere was tense outside parliament as armed guards and riot police ringed the picturesque neighbourhoods around the National Assembly. — Additional reporting AP