French police are preparing as unions and other goups hold nationwide protests against changes to labour laws they fear damage job security.
The protests are the first big public display of discontent with President Emmanuel Macron's presidency, which kicked off in May amid enthusiasm over his promises of revving up the French economy but is now foundering amid anger over the labour decrees and other domestic troubles.
The prominent CGT union is leading the protests, calling for strikes and organising 180 demonstrations against labour decrees unveiled last month by Mr Macron's government.
At the Eiffel Tower, CGT union representative Denis Vavassori said workers will walk out on Tuesday afternoon, but it is unclear whether the monument will be forced to close or will stay partially open for tourists.
Horn-tooting funfair workers held a separate protest in the capital against legal changes they say favour big corporations and could wipe out their centuries-old industry.
Dozens of big rigs drove at a snail's pace around the Arc de Triomphe, causing rush-hour traffic jams as protesters danced and waved flags on a flat-bed truck with a severed plastic head from a funfair ride.
The workers said they timed their protest to coincide with the broader labour demonstrations, since both movements are about workers fearing their jobs are at threat.
Bumper car worker Sam Frechon said: "Everybody likes funfairs. Everybody has been to a funfair one time in his life. Funfair is France."
Thousands of union activists marched on Tuesday morning in the Mediterranean city of Marseille, in Le Havre and other cities.
An afternoon march is planned in Paris, where police announced extra deployments.
While union marches are usually peaceful, troublemakers on the margins often clash with police. A broad movement against similar labour reforms last year saw several weeks of scattered violence.
The protests come amid anger at a comment last week by Mr Macron suggesting that opponents of labour reform are "lazy".
Government spokesman Christophe Castaner said on RTL radio that the president did not mean workers themselves but politicians who failed to update French labour rules for a globalised age.
Mr Macron's labour decrees - which reduce the power of unions and give companies more authority to fire workers and influence workplace rules - are the first step in what he hopes are deep economic changes.
The decrees are to be finalised this month.
Critics say they dismantle hard-fought worker protections and accuse the government of being undemocratic for using a special method to push the decrees through parliament.
Companies argue that existing rules prevent them from hiring and contribute to France's high unemployment rate, currently around 10%.
Some unions refused to join the protests, preferring to negotiate with the government over upcoming changes to unemployment and retirement rules instead of taking their grievances to the street.
Mr Macron himself is in the French Caribbean to meet victims of Hurricane Irma and see the aid operation.