A haptic interface compatible with the Magnetic Resonance (MR) imaging technique allows tracking of the neural correlates of specific haptic interactions and investigations of reparative plasticity in the sensorimotor cortex, with the aid of functional MR imaging (fMRI). In this paper, we present an fMRI compatible haptic interface with pneumatic actuation that has been built up to perform sensorimotor tasks in the MR scanner. It has one translational degree of freedom and is equipped with position and force sensors enabling different position, force or impedance control modes. Pneumatic actuation is magnetic inert in nature, whereas it has high nonlinearity and parameter uncertainties. Stringent MR compatibility requirements limit material choices and thus also the mechanical properties of the hardware. Both aspects bring substantial challenges for the control. A nonlinear sliding mode controller has been designed and tested. fMRI experiments and detailed image analysis have been conducted, demonstrating that the haptic system is safe, brings no image artifact, and functions properly in the MR environment.