Socialist François Hollande, tipped to win the presidential election, immediately promised to introduce a new law, as did incumbent Nicolas Sarkozy.
The court’s decision not only makes the law invalid, it also means that all cases currently being pursued will be dropped.
The justice ministry is to instruct prosecutors to pursue cases on other grounds, such as attempted sexual assault, where appropriate.
The Constitutional Council judged the 2002 definition of the crime as “harassing someone in order to gain sexual
favours”, punishable by up to a year in jail and a fine of up to 15,000 euros, contrary to the constitution’s requirement that to define a crime in “sufficiently clear and precise terms, the court ruled.
It was less precise than the 1992 definition it replaced, which mentioned “abuse of authority”, the judgement said.
The case against the law was brought by a former MP, Gérard Ducray, one of several French politicians to face sexual harassment charges recently.
He was sentenced to a three-month suspended sentence and fined 5,000 euros in 2011.
Ducray argued that the law was too open to interpretation and could lead to convictions for “acceptable flirting”.
But it was also supported by a French-based anti-harassment group, AVFT, which argued that almost all cases were dismissed and called for a deferred suspension of the law so that cases could be pursued until changes were made.
The AVFT called the court’s decision a “frontal attack on women’s rights” and called a protest in Paris on Saturday morning.
The justice ministry says that the crime resulted in about 80 convictions a year.