I don't know about Germany, but in the U.S. it's common that only the union leaders and negotiators get paid their normal salaries during strikes and lockouts. The rank-and-file members get a reduced amount or nothing from the union. (Or sometimes just health benefits.) For example, the recently locked-out American Crystal Sugar workers got a stipend of $100/week and no other benefits. Their normal salaries averaged about $750/week.

It depends on how recently organized the union is, and how secure those members feel and how much of that was afforded by the union. Many members of weaker industrial (not craft) unions are afraid to strike with their brothers.