Paris mayor Anne Hidalgo is considering making the capital's public transport free to all Parisians in a bid to reduce air pollution - but her plan faces opposition from the head of the regional transport authority, who said the move would hit taxpayers.
Ms Hidalgo has launched a study into the feasibility of free city-wide transport, and told French daily Les Echos she wanted to debate the issue ahead of municipal elections in 2020. She told the paper: "The question of free transport is one of the keys to urban mobility in which the place of the polluting car is no longer central".
In a statement, she said the study would work out if there is a viable economic model for free public transport in the capital. A number of other French towns and cities already operate free transport systems.
"I have decided to commission three of my deputies to conduct a vast study on the subject, which will involve French and foreign experts," the mayor announced in a statement.
"Nothing says today that this is possible," she said, adding, "free access for users necessarily implies identifying other sources of funding".
If it does go ahead, the scheme is intended to persuade the 25% of commuters in Paris who use their own cars to get to work to leave them at home in favour of the Metro, local trains, trams or buses.
The free-for-all public transport plan is on top of a scheme to make give free Navigo passes to over-65s whose monthly income is less than €2,200 (€3,400 for couples)
But she face opposition from Valerie Pecresse, head of the Ile-de-France region around Paris and president of the area’s transport authority IDFM - and a possible rival in two years - saying if travellers did not pay, taxpayers would have to do so.
Public transport users in Paris contribute some €3.8 billion to the Île-de-France region's coffers.
Ms Hidalgo did not say whether the free travel plan would cover the 2.2million residents of Paris or all 12million living in the city and Ile-de-France region.
More than 60% of Parisians already use the city's public transport system, according to a 2015 study by EU statistics body Eurostat.
Sign up to our free weekly e-newsletter
Subscribe to access all our online articles and receive our printed monthly newspaper The Connexion at your home. News analysis, features and practical help for English-speakers in France