PARIS (REUTERS) - French commuters face major train service disruptions on Thursday (March 22) due to an unexpectedly large walkout by railway workers angry at the government's plans to shake up the state-owned and highly indebted SNCF rail company.

Labour unions said last week they would launch rolling strikes in early April, but France's transport minister said many were planning to join a wider day of public service protests on Thursday, reducing rail services by 50 per cent.

"There will ultimately be serious disruption tomorrow," Transport Minister Elisabeth Borne said on Wednesday (March 21).

Unions are on a collision course with the government over its plans for the biggest shake-up of SNCF (Societe Nationale des Chemins de Fer) since the nationalisation of the railways in the 1930s. Among the government's plans are the trimming of benefits received by SNCF's 260,000 employees and a cut in its €45 billion (S$72.8 billion) debt.

The showdown was due to start with strikes two days a week over three months from April 3. It is shaping up as the biggest test of Mr Emmanuel Macron's presidency since the 40-year-old came to power last May on a promise of sweeping economic reforms.

Thursday's stoppages are not part of the programmed rolling strikes. They are being organised to dovetail with a day of demonstrations by civil servants and public service employees opposed to plans to change the retirement system.

Minister Borne said the stoppages would halve regional rail services nationally and that high-speed TGV connections between major cities would be cut to 40 per cent of normal levels.