Unions have called for a nationwide day of strikes and demonstrations and hope to repeat the large turnout seen on the first major protest on Jan. 19, when more than a million people marched against the reform. Strikes that day also halted trains, blocked refineries and curbed power generation.

"It will be a difficult, very difficult day for public transport... We expect major disruptions," Transport Minister Clement Beaune said on LCI TV.

National railway operator SNCF said in a statement that traffic would be seriously disrupted on its entire network on Tuesday due to the strike, and recommended that people cancel or delay their travel or work from home.

Tickets already bought for the period between 6 p.m. on Monday Jan. 30 and 8 a.m. on Wednesday Feb. 1 will be fully reimbursed, SNCF said.

RATP, the public transport operator for the Ile-de-France region around Paris, also said metro lines and suburban trains will be heavily disrupted on Tuesday.

French civil aviation authority DGAC said in a statement it had asked airlines to reduce their flight programmes by 20% at the Paris Orly airport on Tuesday, but added that despite this preventive measure delays and disruptions could be expected.

Transport minister Beaune said the government remained open to further talks with unions but he said President Emmanuel Macron's government would maintain the reform's key target of increasing the retirement age by two years to 64.

"The heart of the reform will not change," he said.

The government wants to gradually increase the retirement age by three months per year from September, until 2030, and also plans to increase the length of time workers make social security contributions.

Unions - including the moderate CFDT union - are united against the reform and have vowed to continue strikes and demonstrations until the government drops its plans.

Macron has said he was elected on a platform to reform pensions and that without the changes France's pension system cannot remain financially viable.