France’s president, Emmanuel Macron, shunned parliament and opted to push through a highly unpopular bill that would raise the retirement age to 64 from 62 by triggering a special constitutional power. The risky move on Thursday was expected to trigger a quick no-confidence motion in Mr. Macron’s government and risked plunging France into a prolonged period of domestic unrest.

By Thursday afternoon, thousands of French citizens opposed to both the bill and to Monsieur Macron’s legislative sleight of hand descended on the iconic Place de la Concorde in the center of Paris to protest. That is just the start of what could shape up to be many days of demonstrations and clashes with riot police. 

The newspaper Le Parisien reported that protesters had seized portions of the Ministry of Culture building and possibly a section of another government ministry building in central Paris. 

The special power in question is something called the 49.3 rule, which permits the government to accelerate the passage of a bill that the majority would otherwise appear reluctant to adopt. It has rarely been invoked. 

Le Parisien also reported that at a meeting of the Council of Ministers, Mr. Macron said his “political interest and will was to go to the vote. Among all of you, I am not the one risking his place or his seat. But I consider that as things stand [without the bill], the financial and economic risks are too great.” 

The decision was made just 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. The unpopular plan has prompted major strikes and protests across the country since January.

As lawmakers gathered in the National Assembly Thursday to vote on the bill, the leftist members of the parliament broke into 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 of the parliament as heavily armed guards and riot police ringed the picturesque neighborhoods around the National Assembly.

Earlier Thursday, the Senate adopted the bill in a 193-114 vote, a tally that was largely expected because the conservative majority of the upper house of parliament favors raising the retirement age.

Mr. Macron’s alliance lost its parliamentary majority last year, forcing the government to count on conservative lawmakers to pass the bill. Leftists and far-right lawmakers are strongly opposed and conservatives are divided, which made the outcome unpredictable.

The French leader wants to raise the retirement age so workers put more money into the system, which the government says is on course to run a deficit.

Mr. Macron has promoted the pension changes as central to his vision for making the French economy more competitive, but it is not a vision that everyone shares. Nearly 500,000 people protested against the bill around the country Wednesday.

On Thursday the head of the powerful CFDT trade union, Laurent Berger, called for new demonstrations. Monsieur Laurent tweeted, “By resorting to 49.3 the government is demonstrating that it does not have a majority to approve the two-year postponement of the legal retirement age.” He added, “The political compromise failed: It is the workers who must be listened to when we claim to act on their work.”

Economic challenges have prompted widespread unrest across Western Europe. In Britain on Wednesday, teachers, junior doctors, and public transport staff were striking for higher wages to match rising prices. Spain’s leftist government joined with labor unions to announce a “historic” deal to save its pension system by raising social security costs for higher wage earners.