As any rebellious young Parisian knows, there are many ways to jump the Métro. There is the slick arm-lift-over-turnstiles (upper body strength needed) and the jump-and-tap (if you're tall enough to leap up and trigger the exit sensors). And then there is the preferred method of Parisiennes who make up what they lack in athleticism with abject shamelessness: "Excusez-moi monsieur, can I slip in behind you?"

For most who ride the city's underground illicitly each year, the thrill of Métro hopping is tempered by the threat of being stopped by inspectors and fined up to €72 (£62). For an ingenious minority, however, there is no such deterrent: they pay a small monthly sum into an unofficial insurance fund, or mutuelle, which covers any charges in full.

As well as saving themselves money – members contribute between €5-€7 (£4-£6) a month to the pot, a snip compared with a €53 (£46) Navigo pass – the fare-dodgers believe they are striking a blow to a capitalist system which demands payment for public transport (the RATP transport authorities estimate losses through ticketless travellers at €80m, or £69m, a year).

Many members of the self-styled mutuelles des fraudeurs say they are combining personal financial gain with political idealism. "Why don't we pay for public transport?" asked a recent edition of Lignes gratuites (Free lines), the newsletter read by Paris's dozen or so mutuelles. "Because, just like education and health, we believe that public transport should be . . . free," came the answer.

But, after an article in the newspaper Le Parisien this week, many of the mutuelles have adopted a more reticent tone. They are meeting tonight to discuss how best to put their arguments – aware, perhaps, that it might not be received as warmly by the fare- paying public as by their fellow brothers in arms.

Indeed, Cyndie, an 18-year-old Parisian queuing for the Métro yesterday, said the fraudeurs' claims of an idealistic battle were a con. "It's just unfair because the rest of us have to pay," she said. "It's all very well saying you want public transport to be free, but who's going to maintain the stations and everything else?"