It's stated that the unions in Europe strike because they are stronger than those in the US and the author goes on to say that union membership is stronger in Europe than the US, citing the 20% rate in Germany.

In France the unionization rate is a mere 9% and I would argue that they strike out of weakness and not out of strength...If they were strong they wouldn't have to scare the government by actually striking. They wield a big sword and they use it when they need to remind the governments that they are still there.

There is a reason behind such a low unionization rate in France... Any worker, unionized or not who goes on strike gets the same protections as the union...Additionally, when the union negotiates with companies, the benefits apply to all workers, not just members of the union...Most workers just decide not to pay union fees.

Germany's collaborative system robs the unions of some of their striking power. The union must agree amongst themselves to strike, then they must announce beforehand their intention to strike and in some cases, like this one, the government (or a judge) can refuse their right to strike.