Speaking to La Tribune de Genève, the mayor of the French town, Antoine Vielliard, said they estimated there to be some 20,000 ‘false' residents of France in the Geneva region, and 600 in the commune alone.
Such people live in France and work in Switzerland, but claim to be living in Switzerland.
This means France misses out on taxes. Under a Franco-Swiss agreement on frontaliers, taxes are collected by the Swiss canton where the person works but a third is then given to the French commune where they live.
“We need this money to develop transport, crèches and all the public services that our Swiss residents also benefit from,” Vielliard told the paper.
French towns across the Geneva region are missing out on a total of 40 million euros, he estimates.
There is currently no penalty for self-declaring, but that will change from 2018 when the automatic exchange of banking information comes into effect.
The deadline has already encouraged many to come forward, said the paper.
In two years the number of declared frontaliers in Saint-Julien-en-Genevois has risen from 600 to 1,000, bringing in an additional 600,000 euros in taxes to the commune's coffers.
The campaign includes this video issued by the commune (in French).