The European Commission, the EU's powerful executive, confirmed to AFP on Friday that it had sent a letter to the French government, seeking clarification on a law that puts clear limits on the way Uber can do business in France.
The letter, dated earlier this month, launches the EU's so-called infringement process, which can potentially lead to official charges at the European Court of Justice, the bloc's highest court.
"We are in close contact with the French government to move this case forward," said Jakub Adamowicz, spokesman for the commission.
Sources with knowledge of the matter said the letter consisted of a 17-page questionnaire requesting clarifications on the legal basis of the law.
France has 10 weeks to respond to the questions.
The procedure follows two complaints against France filed with the EU by Uber earlier this year.
Uber's accusations cover a laundry list of claims, most involving European laws on competition and the single market.
Similar complaints were filed in Spain, where Uber is currently banned outright, and Germany. A source said letters from the EU could also be expected in those countries soon.
"Uber is fighting this discriminatory, patchwork treatment. The Uber question can be decided at the European level," said Mark McGann, Uber's head of public policy.
McGann specifically decried the "radically different treatment" of Uber in the 20 EU member states where it so far operates.
"I am confident that the commission is asking the right questions," he said.
An EU source said the goal of the letter was not to overtly back Uber, but to find the right compromise with the angry traditional taxi lobby.
"The objective is to protect public actors as well as taxis, all while maintaining a place for new technologies," the source said.