  The conflict between relativistic causality and localizability is analyzed in
the light of the existence of unsharp localization observables. A theorem due
to S. Schlieder is generalized, showing that the assumption of local
commutativity implies the localization observable in question to be unsharp in
a strong sense. Furthermore, a recent generalization of a theorem of L\"uders
is applied to demonstrate that local commutativity is a necessary consequence
of Einstein causality even in the case of unsharp observables if they admit
local measurements. These findings raise the question whether localization
observables can be measured by means of local operations.
