The concept of unfinished nursing care (UNC) describes nursing interventions required by patients and families that nurses postpone or omit. UNC reasons have been documented; however, no studies have summarised the underlying factors triggering the UNC during the pandemic. Therefore, the aim was to synthesise the available studies exploring factors affecting UNC during a pandemic. We conducted an integrative review following Whittemore and Knafl's framework according to the Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. PubMed, the Cumulative Index to Nursing and Allied Health Literature (CINAHL) and the Scopus databases were searched for primary studies that collected data from 1 January 2020 to 1 May 2023. Both qualitative and quantitative studies assessing the reasons for UNC were eligible and evaluated in their quality using the Critical Appraisal Skills Programme and the Mixed Methods Appraisal Tool. Four studies were included-three qualitative and one cross-sectional. The reasons for UNC have been documented at the following levels: (a) system (e.g., new healthcare system priorities); (b) unit (e.g., ineffective work processes); (c) nurse management (e.g., inadequate nurse manager's leadership); (d) nurse (e.g., nurses' attitudes, competences, performances); and (e) patient (increased demand for care). The reasons for UNC during the COVID-19 pandemic are different to those documented in the pre-pandemic times and reflect a pre-existing frailty of the National Health Service towards nursing care.