Deputy mayor Patrick Klugman confirmed to the BBC on Wednesday that the mayor was "definitely serious" and that action would be taken "in the coming days".
Fox News had rubbed salt into the wounds of the Charlie Hebdo attack, he said, by spreading "totally fake, false information" about the city - including popular tourist areas such as Montmartre.
"It was like a pain after the pain to be insulted by such a lack of fact-checking in broadcasts all over the world," he said.
Legal experts, he added, were currently deciding whether to bring the action in New York or Paris.
A number of legal experts have chorused that the case would be a non-starter in a US court.
"I believe there is no cause of action in the United States, period," Jane Kirtley, a media law professor at the University of Minnesota, told the Reuters news agency.
Patrick Klugman Deputy mayor of Paris
We want Fox News to assume responsibility because they hurt us, they hurt the city of Paris"
"This is an example of someone from another country not recognising the force of the First Amendment, which allows criticism of governmental entities," she said, referring to part of the US Constitution, which guarantees freedom of speech and freedom of the media.
But what about a French court?
London-based media barrister Matthew Nicklin QC says there would be serious obstacles.
Unlike a person or company, he says, the "city of Paris" is not a legal entity - it cannot sue for defamation. What it might be able to do, he says, is to help bring a "representative claim" on behalf of individual Parisian businesses.
These businesses would have to prove that they had been negatively affected as a result of the Fox News item - by suffering financial losses, for example.
Fox has already accepted that the report was incorrect, with an anchor apologising on air for the channel's "errors".
The next difficulty would be deciding which end of Fox News to sue.
We've all moved on - end of story James McKay Birmingham city councillor
No US-based network would submit to French jurisdiction, Nicklin says. And while it might be technically possible to sue a part of Fox News based in France, it would be necessary to demonstrate that this French part of the company was in charge of Fox's coverage at the time.
If Paris did succeed in overcoming these hurdles, any court would take into consideration that Fox News offered apologies, both to Paris and Birmingham - which was described by pundit Steve Emerson as "totally Muslim, where non-Muslims just simply don't go in".
The prospects of achieving compensation are much diminished when apologies are offered quickly and repeatedly, Nicklin says.
"The comments about Birmingham were a bit bonkers. We said so. Fox News corrected them. We've all moved on. End of story," Birmingham city councillor James McKay said on Wednesday, making clear that the city would not take part in the Parisian legal action.
There are two other difficulties standing in Paris's way.
One is the European Convention on Human Rights, which enshrines the right of freedom of expression. If the case ever came to court, Fox News would point out that France is a signatory.
Then there is a US law passed in 2010 - the Speech Act - which gives media outlets special protection against decisions of foreign courts.
"Even if a judgment were obtained in France, it would be impossible under American law to enforce it here," Robert Drechsel, a professor of media law at the University of Wisconsin at Madison told Reuters.
But Klugman, a lawyer before he became deputy mayor, appeared undaunted. He disagreed with Nicklin's assertion that Paris was not a legal entity, saying the city could "take anyone to justice and… has done it many times".
"Our logic is very simple," he said. "We want Fox News to assume responsibility because they hurt us, they hurt the city of Paris."http://www.bbc.com/news/magazine-30918379