Impurity operators in RSOS models

We give a construction of impurity operators in the 'algebraic analysis' pi cture of RSOS models. Physically, these operators are half-infinite inserti ons of certain fusion-RSOS Boltzmann weights. They are the face analogue of insertions of higher-spin lines in vertex models. Mathematically, they are given in terms of intertwiners of U-q ((sl) over cap (2)) modules. We pres ent a detailed perturbation theory check of the conjectural correspondence between the physical and mathematical constructions for a particular simple example.