The transverse single-spin asymmetry A_N observed in high energy proton-proton collisions p^uparrow p to pi X has been found to increase with the momentum fraction x_F of the pion up to the largest measured x_F sim 0.8, where A_N simeq 40%. We consider the possibility that the asymmetry is due to a non-perturbatively generated spin-flip coupling in soft rescattering on the target proton. We demonstrate using perturbation theory that a non-vanishing asymmetry can be generated through interference between exchanges of even and odd charge conjugation provided both helicity flip and non-flip couplings contribute. Pomeron and odderon exchange can thus explain the energy independence of the asymmetry and predicts that the asymmetry should persist in events with large rapidity gaps.
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