The bill was approved by France’s lower house last July, but was yet to be approved by the Constitional Council.
Under the bill, social media groups have faced fines of up to 4% of their worldwide income for not having to remove in a day “manifestly illegal” content related to the race, sex, religion, sexual orientation or disability.
Several free speech advocacy groups had argued that the bill could pave the way for state censorship because it does not clearly define illegal content.
“(These measures) undermine the exercise of freedom of expression and communication in a manner that is unnecessary, inappropriate and disproportionate,” the court said.
The court, which is the French equivalent of the US Supreme Court, cited 1789 “Declaration of Human and Citizen Rights” which is the preamble to the constitution.
He noted that the bill provides that the administration would have had the lead role in their decision on the illegal content, without the intervention of a judge.
This could push corporate social media to remove more online content than necessary for fear of punishment, he said. The court also said that the 24 hour window time was “particularly brief”.
The court also slapped another provision of the bill, under which any content considered to be child pornography, or terrorists in the wild, should have been removed within an hour.
Facebook and Twitter did not immediately respond to requests for comment.