Especially if they're diesel.
Cars have been getting a lot cleaner in recent years, with emissions from newer cars being significantly lower than those made even relatively recently. These slightly older vehicles have become a target for Anne Hidalgo, the mayor of Paris, who wishes to clean up the significant smog problem faced by the city. So by July, trucks and buses registered before October 2001 will be banned from driving in the city limits between the hours of 8 am and 8 pm.
By the middle of next year, the ban will expand to all vehicles made before 1997, and rather puzzlingly, motorcycles from before 2000. By 2020, the ban will even include diesel cars from before 2011. Harsh rules make a certain amount of sense, as even though they get good mileage diesels produce a lot more particulate emissions than gasoline engines. But bikes have never been identified as a major contributor to smog. About 1 in 7 of Paris's vehicles will be affected by this ban, and those who rely on these vehicles will get a 500-Euro check to go toward the purchase of something newer. Fat lot of good that'll do.