First of all, the strike is a bad deal for Fiat Group.
Second, don't jump to conclusions based on a single statistic. For one thing, we don't know the timeframe involved. Are they comparing to the previous month? The same month or quarter of the previous year? Year to date compared to last year?
Fiat has had three hits and three flops recently and they are all runing at the same time. The Panda, Grande Punto and the 500 are the hits. the Idea, Croma and the Bravo are the flops and the Stilo was also a recent flop. Actually, it's a current flop as well since the Stilo Break is still on offer.
The Alfa 147 and 166 have been around too long. The 159 is not exactly best in class and is overpriced. The two seaters seem to be doing well.
The Lancia range is basically dead and should probably be done away with.
Given the above, it would not be surprising if sales were down by 18% in Italy as the flops outweigh the hits. On the European level, Fiat is in sixth place in the sales race. Again, don't read too much into a single statistic that covers a single area.