Trade unions play a very important role in the employment relations systems. Whistleblowing occurs in this same sphere suggesting that trade unions will be involved. However, what is known about trade unions in this space is either theoretical or empirically limited. This chapter seeks to explore these dynamics by exploring the limited literature to shed light on what we know about trade unions in practice. It will draw on the recent UK Post Office Horizon IT scandal. It will show how the theoretical discussions in the literature using Individual, Collective and Public Union voice maps to an extent what we have seen in practice. It draws out the difficulties trade unions face in supporting individual whistleblowers while having a collective mindset. The chapter uses examples from trade union engagement in other spheres of the employment relationship at the three levels to highlight the potential trade unions to take up and support whistleblowing.