French public sector workers went on strike Tuesday, disrupting train services and schools in another challenge to President Nicolas Sarkozy after his party's stinging election defeat.

France's major unions called the national day of action to protest job cuts and plans for pension reform, a centrepiece of Sarkozy's agenda for the second half of his mandate.

The protests came a day after Sarkozy dismissed his labour minister and reshuffled his cabinet in response to a humiliating defeat by the left in regional elections.

Paris area commuters faced some disruption with half of trains running on some suburban lines, while the state-owned SNCF rail authority said nearly two-thirds of high-speed TGV trains were up and running.

One in five primary and high school teachers went on strike, the education ministry said around midday, as unions called for a strong turnout to protest the government's plan to replace only half of retiring staff.

France's biggest union, the CGT, said 180 protest marches were planned in cities and towns across the country.

Union leaders dismissed the reshuffle, saying it would do nothing to revive the economy and accusing Sarkozy of failing to understand that the mood had changed in France.

"Ever since Sunday we have heard (the centre-right) say 'we are going to maintain our course'. They aren't listening and that poses a real problem," said Bernard Thibault, head of the large CGT union which is leading Tuesday's protests.

He urged Sarkozy to call labour leaders and employers together to discuss ways of boosting salaries, and warned the government to expect determined opposition to its planned overhaul of the state pensions system.

"I am convinced that we cannot impose a pensions reform that is based exclusively on accounting and financial criteria," he told Europe 1 radio. "A reform will be very complicated."

Talk of raising the retirement age has been taboo in France where the right to a pension from age 60 has been enshrined since 1982, a legacy of Socialist president Francois Mitterrand's administration.

On Monday, Sarkozy sacked Labour Minister Xavier Darcos who suffered a heavy defeat in the western region of Aquitaine, replacing him with Eric Woerth, who will now be the point man on pensions reform.

Francois Baroin, who had served as a minister during Jacques Chirac's presidency, was appointed to replace Woerth as budget minister. His appointment was seen as a bid to appease the centre-right members of the party.

Two other centre-right UMP members were named to junior posts: Georges Tron as minister responsible for the civil service and Marc-Philippe Daubresse as minister responsible for youth and anti-poverty measures.

Sarkozy was elected in 2007 on promises to boost France's economy and get people back to work, but last year's recession has driven unemployment up to 10 percent, its highest level in a decade.

Many observers saw Sunday's electoral defeat for the government as a verdict both on Sarkozy's policies and his style.

The Socialist-led opposition beat Sarkozy's Union for a Popular Movement (UMP) party by around 54 to 36 percent in the vote, leaving the left in control of 21 of France's mainland regions.

Talks with unions are due to begin in the next few weeks.

Agencies