French President Nicolas Sarkozy has outlined controversial plans to overhaul the pension benefits of half a million mainly public sector workers.
Mr Sarkozy says France needs to work harder
Similar reforms led to weeks of protests in 1995, and unions have hinted there could be more disruption.
Mr Sarkozy plans to cut back the packages given to employees such as train drivers and electricity workers, who until now could retire early.
At the same time, the French parliament debated immigration reform plans.
Mr Sarkozy said he would negotiate with unions and companies but was determined to reform the system without delay.
He also promised to relax further the conditions of the 35-hour week.
The move is part of a wide-ranging plan for social reform, aimed at boosting the country's economy.
Mr Sarkozy insisted special retirement packages given to certain public employees were too expensive for the social security system, and said it was time to align them with the rest of the public sector.
"At the very least, the objective must consist in harmonising the special regimes with that of the civil service, which was reformed in 2003," Mr Sarkozy said.
He also criticised hefty social security payments, saying that handouts discouraged people from working, and stressed his belief that France needed to work harder.
"The system is financially unsustainable," Mr Sarkozy told journalists.
Trade unions reacted angrily. Bernard Thibault, head of the CGT union, condemned the president's plans as "totally unbalanced".
Another group, Force Ouvriere, said the move would lead to the "partial privatisation of the social system".
Attempts to reform pension privileges has brought down previous French governments.
In 1995, an effort by then-Prime Minister Alain Juppe to bring the public-sector regimes closer to private-sector provisions was withdrawn, following a wave of protests.
Mr Sarkozy's announcement came as the French parliament debated proposals to tighten entry conditions for the relatives of immigrants who want to join their families in France.
Under the new bill, immigrant families will have to prove they are solvent financially and can speak French.
In some cases, the legislation would require the relatives to take a DNA test to prove their applications were genuine.
Mr Sarkozy has set up deportation quotas, promising to send home 25,000 illegal immigrants this year alone.
The bill would require immigrant family members aged over 16 to take a test in their country of origin, demonstrating a good knowledge of French language and values.
Applicants would also have to prove their family in France could support them and earn at least the minimum wage.
If immigration officials doubt an applicant is truly a genuine relative of the person he or she seeks to join in France, that person could be asked to take - and pay for - a DNA test to prove a biological link with other family members.
Civil liberties groups say the bill is inhuman, but the government has vowed to clamp down on illegal immigration.