Images on social media showed officers assaulting a young man with truncheons and fists, throwing him to the ground, and kicking him while crushing his legs under their boots.
The same group of police were shown in Rennes capturing and dragging a man to the ground after he appears to have lost consciousness, with his wrists bound.
Other photos on social media show Republican Security Companies (CRS) dragging a protester on the ground for several meters before apprehending her.
Another social media image from Rennes showed the CRS dragging an elderly man whose face was bleeding, as well as a young woman, whom they held by her hair.
Many major media outlets in France have yet to broadcast these images.
Hundreds of complaints were filed on March 31 over arbitrary arrests during the protests in France.
Nearly 1,500 people gathered at the Rennes center to protest the government's controversial reforms.
Police used tear gas on protesters after a clash in which some cars and waste containers were set on fire, according to media reports.
Authorities said a gendarmerie officer was injured.
French Prime Minister Elisabeth Borne said the government is determined to accelerate other reforms.
The controversial pension reform plan was signed and officially promulgated Saturday in the Official Journal.
President Emmanuel Macron signed the bill after the Constitutional Council finished its review late Friday despite demands by trade unions to drop the measure that has drawn weeks of protests.
The nine "sages," as they are known in France, partially approved the bill while rejecting six of its measures, including regarding senior workers.
The bill includes raising the retirement age from 62 to 64 by 2030, with workers and trade unions, among others, vehemently opposing the plan.
The government unveiled the reform proposal in January and it was taken up for parliamentary debate the following month even as millions took to the streets to oppose it.
Unrest intensified when Borne, after consulting with Macron, decided to use special constitutional powers to adopt the bill without parliamentary approval in March.
The decision was driven by fear that lawmakers would be able to block the reforms as the government lacks an absolute majority in the legislature.
