PARIS — Garbage collectors, utility workers and train drivers are among people walking off the job Tuesday across France to show their anger at a bill raising the retirement age to 64, which unions see as a broader threat to the French social model.

More than 250 protests are expected in Paris and around the country in what organizers hope is their biggest show of force yet against President Emmanuel Macron’s showcase legislation, after nearly two months of demonstrations. The bill is under debate in the French Senate this week.

Unions threatened to freeze up the French economy with work stoppages across multiple sectors, most visibly an open-ended strike at the SNCF national rail authority.

Commuters packed into one of the rare trains heading for Paris from the southern suburbs before dawn. The government encouraged people to work from home if their jobs allow.

A fifth of flights were canceled at Paris’ Charles de Gaulle Airport and about a third of flights at Orly Airport. Trains to Germany and Spain are expected to come to a halt, and those to and from Britain will be reduced by a third, according to the SNCF rail authority.

More than 60% of teachers in primary schools are expected to be on strike, as well as public sector workers elsewhere.

The reform would raise the official pension age from 62 to 64 and require 43 years of work to earn a full pension, as France’s population ages and life expectancy lengthens.

Opinion polls suggest most French voters oppose the bill. Left-wing lawmakers say companies and the wealthy should pitch in more to finance the pension system.