O-type stars display rotational modulation of their photometric brightness due to surface features induced by fossil magnetic fields, and possibly through dynamos driven by subsurface convection. These features introduce wind perturbations that may drive large-scale structures and flows, including magnetospheres and corotating interaction regions. Until recently there has been a lack of high-precision, high-cadence photometry of O stars capable of detecting this variability. The wealth of new observations provided by the Transiting Exoplanet Survey Satellite (TESS) offers an unparalleled opportunity to conduct comprehensive studies of O-star variability at the sub-mmag level. Using the Galactic O-Stars Catalogue (GOSC) we have identified a sample of confirmed Galactic O stars observed by TESS with existing high-resolution spectroscopy from the IACOB and OWN surveys. Frequency analysis of the photometry is preceded by a careful examination of potential blending sources. Existing spectroscopy of each candidate is employed to test the rotational modulation hypothesis. In this presentation we describe the preliminary results of our study and outline plans for future analysis.