Sonas has claimed it took over two weeks for testing to occur after the first resident with symptoms was identified.
The nursing home group claims chief inspector of social services Mary Dunnion failed to take this delay into account in making her findings.
It also claims the failure of a HSE Outbreak Control Team to offer staffing support, when so many workers were out with the virus, was not taken into account in the report.
The group, which operates 11 nursing homes and four retirement villages around the country, fears the publication of the report would cause “grave reputational damage”. It was due to have been published on the website of the Health Information and Quality Authority (Hiqa) last October, but this did not occur after Sonas indicated that judicial review proceedings would be brought.