French postal workers have gone on strike, launching days of public sector walkouts that will also hit the railways and electricity grid.
There were scuffles near the home of UMP leader Nicolas Sarkozy
The postal unions are angry at plans to open up the service to outside competition in line with EU directives.
Trade unions said some 20% of their staff had joined the one-day strike, but employers put the number at 15%.
Rail workers also began their one-day action late on Tuesday, that is set to bring chaos to France's railways.
Electricity workers will stage walkouts on Wednesday, with teachers and other civil servants protesting on Thursday.
The strikes are being seen as an important test for the centre-right government of President Jacques Chirac.
The unions say the government's economic policies are a threat both to the public sector and to the purchasing power of working men and women.
Their demands include higher wages, and an end to moves to relax the 35-hour working week.
Unions have repeatedly warned that plans to introduce competition into mail delivery will force many rural post offices to close.
French rail travellers are now braced for severe delays and cancellations
They are also protesting against what they described as a creeping privatisation.
"Public service, yes! Privatisation, no!" hundreds of postal workers chanted outside parliament in Paris on Tuesday.
There were scuffles with police when some 80 workers led by the head of the Trotskyist Revolutionary Communist League (LCR), Olivier Besancenot - himself a postman - demonstrated near the Paris home of Nicolas Sarkozy, leader of the governing Union for a Popular Movement (UMP) party.
Rail workers also began their industrial action late in the day, fighting against the predicted loss of more than 3,000 jobs this year.
The unions warned of severe disruptions, with only one in four suburban trains serving the capital and one in three high-speed TGV operating.
Regional services were also set to be badly hit, but the Eurostar link with Britain was not expected to be affected, the unions said.
Pressure on government
French unions, which are as powerful in the state sector, say that the mood of the public is shifting against the government's policies of economic liberalisation, however cautious these may be.
And they point to an opinion poll suggesting that 65% of the population support the protest movement.
But correspondents say the strikes are as much a test of the unions as they are of the government, to see if they have the strength for a more extended campaign later in the year.
However, President Chirac's government says it has no intention of backing down on what it says are much-needed economic reforms.