French police have banned "yellow vest" protesters from the Champs-Élysées in Paris on Saturday after rioters destroyed businesses last week.
The government has warned that it intends to react severely against any new outbreak of violence.
The government for the first time is deploying soldiers to help maintain security, both in Paris and in Nice.
But there has been widespread criticism over anti-terrorist forces being used as crowd control.
A soldier from the anti-terrorism Sentinelle patrol force told the Franceinfo website of their discomfort at being deployed to control the protests.
"Sentinelle guys are all soldiers - we don't know how to keep order," the soldier said, speaking on condition of anonymity.
Politicians from across the political spectrum also voiced concerns.
Bruno Retailleau, leader of the main opposition Republicans in the Senate, told the France 5 television channel that the decision was a "serious mistake".
The "yellow vests" ("gilets jaunes") started protesting in November, initially because of fuel tax rises.
The movement soon evolved into a broader rebellion against perceived elitism, for which activists blame President Emmanuel Macron.
Could the protests escalate further?
Last Saturday shoppers and tourists watched in horror the scenes of lawlessness along the Champs-Élysées, as groups of rioters looted and burned with police seemingly powerless to intervene. The government says that can't be allowed to happen again.
So for this Saturday, the Paris police chief has been replaced, fines for illegal assembly have been increased, and the area around the Champs-Élysées has been declared off-limits.
For the first time soldiers, normally on anti-terrorism patrols, are to be deployed outside public buildings in order to free up police.
But that's raised worries about what happens if troops, armed with assault rifles and untrained for riot control, find themselves cornered by a mob.
The government says it won't happen because police will always intervene first.
Maybe - but the main lessons from four months of yellow vest protests in Paris is that they move quickly from place to place and are very unpredictable.
Following last week's riots, which resulted in more than 120 arrests, Mr Macron vowed "tough" action.
Paris police chief Michel Delpuech was replaced by Didier Lallement, the top police official in the south-west Nouvelle-Aquitaine region.
Money has been raised for owners of kiosks that were burned out and some were being replaced on Friday.
Burned-out press kiosks on the Champs-Elysées are being replaced today. Good news. The project manager for the company (owned by JCDecaux) said it's their last batch, so they're crossing fingers ahead of tomorrow's Gilets Jaunes protest. pic.twitter.com/JzwihUFw6z— Stanley Pignal (@spignal) March 22, 2019
Concessions were offered to protesters late last year as the movement was picking up speed - including €10bn (£8.5bn; $11bn) designed to raise incomes of the poorest workers and pensioners. But this has not put an end to the riots.
For the past month the president has toured France, listening to local mayors and citizens as part of his "grand débat" - a big national debate.