Paris Mayor Anne Hidalgo is commissioning a study into making public transport free in the French capital to bring down grim levels of air pollution, reports RTE.
The study will see politicians and experts report back by the end of the year on whether the scheme would be financially feasible.
The socialist mayor also said she has further negotiated discounts at park-and-ride stations to encourage commuters to leave their cars on the outskirts.
Paris could build a transport policy around free public transport "in which polluting cars no longer play a central role," she told Les Echos newspaper.
Ms Hidalgo has made a priority of tackling smog and is planning stricter rules aimed at phasing out diesel cars by 2024, when Paris will host the Summer Olympics.
The study will also look at the possibility of introducing a toll, like London's congestion charge, as she seeks to discourage motorists from driving into Paris.
But her announcement prompted accusations of electioneering from opponents at a time when she is under fire over her management of the city, particularly on transport.
Her flagship policy of banning cars along a stretch of the River Seine was overturned by a court ruling last month which she has been forced to appeal.
And the city's popular Velib hire bikes have been virtually absent from the streets since January due to a botched handover to a new contractor.
Valerie Pecresse, the conservative head of the wider Paris region, said she was "open to all new ideas" but warned Ms Hidalgo against "going it alone" on free transport.
Ticket sales bring in 3 billon euros per year, Ms Pecresse told Radio Classique, adding she would not settle for "a euro less".
Julien Bargeton, a senator from President Emmanuel Macron's Republic on the Move (LREM) party, said the announcement amounted to a "campaign launch" for 2020 municipal elections.