The role of a ∑3{1 1 2} incoherent twin boundary (ITB) on the shear stress of Cu at the micron scale has been investigated through microcompression of bi-crystalline pillars containing ITB, as well as single-crystalline pillars, in two different compression directions. The Cu sample containing ITBs was synthesized using magnetron sputtering on a sapphire substrate. Firstly, pillars along [1 1 1] compression direction were milled on the film surface. As multiple slip systems were activated upon loading, the dislocation-ITB interaction in this direction was dominated by the dislocation–dislocation interactions. Another set of pillars was milled from the side of the film (in the thickness of the film) in a nominally [134¯] compression direction. Compression in this direction activated a single slip in each grain, which facilitated the investigation of the interaction between dislocations and ITBs. Post-mortem images showed that slip traces were not distinctly connected at the boundary unlike ideal slip transmission in pillars containing a coherent twin boundary. Moreover, bi-crystalline pillars in the single slip direction are stronger than single-crystalline pillars. The observations indicate that ITBs are not impenetrable for dislocations, but the boundary demonstrates some resistance to transmission.