[MrDresden]

Icelander here. We have 90+% union participation in the country. A large portion of certain unions are immigrant workers. They have at numerous times gone on strike for better pay.

So, at least here, your hypothesis does not seem to hold.

This is probably due to the unions educating those immigrant workers on what their rights are.

[bbarn]

Iceland also has very bizarre "union" structures that more resemble professional associations than unions in other countries. When I worked at a software company in Kópavogur, on my team of 7 there were at least 4 different unions represented.

[MrDresden]

I'm not sure bizarre would be the way I'd describe it, but it is probably not identical to how the setup is everywhere else.

There are those that fit the professional association description, for instance the union of computer scientists which mandates a university degree in cs to become a member (this union does do collective bargaining with government and municipalities but not private enterprises), but then there are more broader unions for bigger sectors that do collective bargaining against the industrial collective (samtök atvinnulífsins).

So, I'm not sure what is with the downvotes for bbarn's comment. Its a point that isn't far off.