Reuters Business Report - Sex sells - but a new law under debate in France could mean penalties for those buying it.
Parliament is considering introducing fines of 1,500 euros for visiting a prostitute, 3,000 for a repeat offence.
These demonstrators say it will punish their profession.
Guy Geoffroy, a member of parliament who is helping sponsor the bill, argues that restricting the client - not the sex worker - gets to the heart of the problem.
MEMBER OF PARLIAMENT AND PRESIDENT OF THE SPECIAL COMMISSION OF INQUIRY INTO PROSTITUTION, GUY GEOFFROY
"There is one aim, only one, and that is to drive back prostitution because it's about one person being dominant over another through the use of money. For many years it has also been a symptom of the scandal of the trafficking of human beings."
These sex workers and their supporters say they should be the ones who control their bodies - and the law will make things worse.
Some claim it will force them to emigrate.
Others say their work serves a social good.
FORMER CLIENT THIERRY
"It's needed, prostitution is a safety valve, it can prevent rape, murders, sexual assaults, even divorce. And there's a part of the population which has no sexual life and without prostitutes what would they do?"
The demonstrators are backed by Ecologist MP Barbara Pompili - who argues the problems associated with prostitution will become harder to diagnose.
ECOLOGIST PARTY MEMBER OF PARLIAMENT BARBARA POMPILI
"You risk driving them even further underground, putting them even more at the mercy of their clients. They're more likely to meet them over the internet, so they're not able to evaluate the clients, so this law, this measure, doesn't solve anything."
For their part, the ruling Socialists are confident of gaining a majority for the bill - some comparing the situation to neighbouring Germany.
Liberalisation of the sex trade there has, say its critics, led to a mega business - with some 400,000 prostitutes serving one million clients a day according to some estimates ....
... a situation that recently led one UK magazine to describe the country as a giant brothel.
By comparison, France has an estimated 20,000 sex workers.
Popular support for the bill is also thinner on the ground - one recent survey finding only 22 percent of French people in favour of the fines.