In this paper, we present a predicate abstraction for programs for programmable logic controllers (PLCs) so as to allow for model checking safety related properties. Our contribution is twofold: First, we give a formalization of PLC programs in first order logic, which is then used to automatically derive a predicate abstraction using SMT solving. Second, we employ an abstraction called predicate scoping which reduces the evaluation of predicates to certain program locations and thus can be used to exploit the cyclic scanning mode of PLC programs. We show the effectiveness of this approach in a small case study using programs from industry and academia.