Inspired by an advert in the Economist, I found this from invest-in-france.org:
New French labour regulations have been brought in and provide incentives to work more and earn more.
Companies can raise the number of hours worked by management staff or independent salaried employees from 218 days to 235 days (and even up to 282 working days if there is collective agreement for working on Saturdays).
Also, since October 2007, employees benefit from exemptions on tax and social security contributions for overtime hours worked over and above the legal working week, effectively an increase of 25% in pay for overtime. The employer also benefits from a flat reduction in employer social security charges for each additional overtime hour.
Our government has work to do to catch the French in liberalising labour laws. Who would have thought it?