PARIS (AP) — France's prime minister is holding special meetings Sunday about the government's divisive redesign of the national retirement system, amid warnings that strike-related transport troubles will get even worse in the coming days.

Travel tangles continued Sunday as the strikes entered their fourth day, with most French trains at a standstill. Fourteen of Paris' subway lines were closed, with only two lines — using automated trains with no drivers — functioning. International routes also suffered disruptions.

Monday will be a bigger test of the strike movement's strength, and of travelers' patience. Unions are calling for even more people to walk off the job Monday, when commuters go back to work. Many people worked from home or took a day off when the strike began last week, but that's not sustainable if the strikes drag on.

Warning of safety risks, the SNCF national train network and Paris transit authority RATP warned travelers to stay away Monday instead of packing platforms for the few functioning trains. “On December 9, stay home or find another means of locomotion,” SNCF said in a message to travelers.

Looking ahead to a challenging week, Prime Minister Edouard Philippe is holding meetings Sunday afternoon and evening with government ministers involved in the reform — and with President Emmanuel Macron, according to government officials.

Macron, a centrist former investment banker, argues that the retirement overhaul will make a convoluted, out-dated system more fair and financially sustainable. Unions however see the reform as an attack on fundamental worker rights, and fear people will have to work longer for smaller pensions.

The government says it won't change the official retirement age of 62, but the plan is expected to include financial conditions to encourage people to work longer, as life spans lengthen.

New nationwide protests are scheduled Tuesday, and the prime minister is scheduled to release details of the plan Wednesday.

Yellow vest activists joined in the anger Saturday, as they added the retirement reform to their list of economic grievances in protests around the country. Police fired tear gas on rowdy protesters at largely peaceful marches through Paris and the western city of Nantes.