Starting this year, the government in France has annulled some of the exceptions to the social security contributions for seasonal workers that the agricultural employers have previously enjoyed. In other words, it is now more expensive to bring in temporary labour for harvesting, pruning and other work in the vineyards or in the cellar.
The exception that is now annulled is contribution for accidents at work and occupational diseases. These will now have to be paid by the employer. But only if you are generous and pay your workers more than 1.25 x Smic. Smic is the French minimum wage which now is 9.43 euro per hour. If you pay SMIC + 25% or less, the exception remains.
Champagne producers have protested loudly as they apparently pay their seasonal workers more than in other regions. We would guess though, that most people hired for harvesting and other tasks are paid Smic and no more.
Read about the new rules here agriculture.gouv.fr