Of the 142 people who were arrested on 12 December, including 124 who were taken into custody, "nearly 80 percent faced no charges in the end", according to a study by the French branch of the international rights watchdog.
A similar proportion of detainees to criminal charges was seen during the Yellow Vest movement that peaked in late 2018 and early 2019, according to Paris prosecutor Remy Heitz.
Amnesty International France (AIF), which joined an umbrella group opposed to the security bill, said it had "legitimate concerns over the possibility that there were arbitrary arrests and other violations of human rights".
The legislation, which has since been scrapped, would have restricted publication of photos of on-duty police officers, a move condemned as a curb on press freedom.
No notable violence before police action
AIF's Anne-Sophie Simpere, author of the report, told the French AFP news agency that the 12 December protest march in central Paris did not see "notable violence," adding: "Nothing seems to justify what happened in terms of arrests or charges."
#DirectSenat Le débat sur les drones de #surveillance part sur leur utilité pour constater les atteintes à l'environnement, pour les sauvetages en montagne... Sauf que dans la #PPLSécuritéGlobale, ce ne sont pas ces objectifs précis, nécessaires et proportionnés qui sont prévus
— Anne-Sophie Simpere (@asimpere) February 3, 2021
The report focused on police questioning, medical certificates and judicial documents in 35 cases of people who were held but not charged. Two were detained for nearly five hours, while the other 33 were held overnight.
A heavy police contingent preceded the marchers and flanked them on both sides, preventing any of them from leaving the protest, AFP journalists reported at the time.
On the basis of witness testimony and video footage, Amnesty said arrests were not preceded by "audible warnings" and at moments when no "significant disorder" was noted in the march.
Police advanced without reason or warning
Alexis Baudelin, a lawyer who was taken into custody, told AFP: "I was surprised by the strategy ... at each intersection, the security forces charged on non-violent demonstrators without reason or warning."
The offensive tactic was aimed at preventing the formation of "Black Bloc" anarchist groups after two consecutive weekends of violent demonstrations in Paris, the police said later.
Amnesty also pointed to "detentions based on vague laws", notably one against "taking part in a group with the aim of planning violence", cited in 25 of the cases studied.
In only two of the cases studied had the detainees been carrying objects that could justify suspicions of violent intent.
