This study examined the association of three specific COVID‐19–related workplace stressors (percentage of nursing work with COVID‐positive [COVID+] patients, number of COVID‐19–related patient deaths witnessed, and living separately from family for safety) and their associations with posttraumatic stress symptoms (PTSS) and symptoms of major depressive disorder (MDD) and generalized anxiety disorder (GAD) among 391 nurses (93.6% White, 93.4% utilize she/her pronouns). Cross‐sectional data were collected via an online survey. Institutional betrayal (i.e., the perception that an institution failed to protect a member who depends on and trusts it) was examined as a moderator of these associations. Although institutional betrayal was not a significant moderator in the three individual models, it held small‐to‐medium–sized positive main effects with PTSS and symptoms of GAD and MDD in both the individual and combined models. In the individual models, the percentage of nursing work with COVID+ patients was significantly positively associated with all three mental health conditions, f2 = .019–.195, whereas it only showed a significant effect with PTSS in the combined model, f2 = .138. Living separately from family was significantly positively associated with PTSS and MDD symptoms in both the individual, f2 = .037 and .015, respectively, and combined models, f2 = .025 and .013, respectively. Number of patient deaths held a significant positive association with PTSS alone, f2 = .022, in the individual model only. The findings are discussed in light of ways in which health care settings can better support and prioritize mental health among nursing staff.