Unionizing rhymes with:
immunizing, antagonizing, dehumanizing, demonizing, galvanizing, harmonizing, hellenizing, humanizing, immunizing, ionizing, organizing, patronizing, reorganizing, revolutionizing, scrutinizing, synchronizing, womanizing
Unionizing sounds like:
unassuming, unceasing, unconscious, uneasiness, uneconomic, uniqueness, unisons, unknowing, unknowns, unsung