Transport for London, which operates the city's tube and bus networks, said Monday it had rejected the ad by Normandy's regional government because it "did not fully comply with its advertising guidelines."
It said the advertisement included messages relating to "matters of public controversy or sensitivity."
The campaign featured a fake newspaper page with a headline "British business owners can now vote with their feet and leave post-Brexit fears behind." It described Normandy as a "friendly region" that makes it "easy for British business to prosper in Europe."
TFL declined to explain why it thinks the advert could be controversial.
With Brexit just 13 months away, many businesses are preparing for a traumatic separation.
Little has been agreed on the future trading relationship between the UK and European Union, and whatever the outcome of the negotiations, there will be new barriers to trade after Brexit.
If the two sides fail to agree a new trade deal, British exporters will face additional costs of £27 billion ($37.5 billion) a year after Brexit, consultancy Oliver Wyman and law firm Clifford Chance estimated in a new report on Monday.
Some companies have already started shifting jobs and investments away from the UK to make sure they will be able continue to trade freely across the remaining 27 EU members after Brexit.
Euroclear, a company that holds huge volumes of shares for stock buyers, said last week it would shift its legal home from London to Brussels.
Cities across the EU are rolling out the red carpet to welcome the newcomers.
In 2016, Paris' La Defense business district took out an advertisement at London's Heathrow airport. Frankfurt, the financial capital of Germany, has advertised in the UK, as has the Dutch city of Amsterdam.
A group representing the French financial industry last week issued invitations to a conference in New York that will highlight the benefits of doing business in Paris. It asked attendees to register using the user name "Brexit."
In total, TFL rejected 23 advertisements last year, according to its annual report. Eight were refused because they were "likely to cause widespread or serious offense to reasonable members of the public." Six were banned because they depicted people in a sexual manner.
At the same time, TFL ran three advertising campaigns by Russia's pro-Kremlin broadcaster Russia Today (RT) last year. Those ads earned TFL £310,000 ($429,000), but significant criticism too.
RT's London marketing campaign came after Twitter announced it would stop accepting advertising from the broadcaster at the height of the foreign agent registration controversy in the US.
Last year, RT was singled out in an intelligence community report for the impact it may have had on the 2016 US election. The report said RT "conducts strategic messaging for [the] Russian government" and "seeks to influence politics, [and] fuel discontent in the US."
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