Background: The COVID-19 pandemic has led to disruptions in cancer treatment delivery among breast cancer patients in the U.S. However, it is currently unknown whether racial/ethnic disparities exist in cancer treatment disruptions among patients with breast cancer and SARS-CoV-2 infection. Methods: We obtained data from the ASCO Survey on COVID-19 in Oncology Registry (March 2020-July 2021) describing breast cancer patients diagnosed with SARS-CoV-2 during their care treated at 46 practices across the US. Data included patient demographics, SARS-CoV-2 diagnosis and treatment, breast cancer characteristics, and modifications to cancer treatment plans. Breast cancer treatment delay or discontinuation (TDD) was defined as any treatment postponed more than two weeks from the originally scheduled date. We computed adjusted odds ratios (aOR) using multivariable logistic regression, accounting for non-independence of patients within hospitals to evaluate racial/ethnic disparities of TDD. Multivariable models were adjusted for age, sex, number of comorbidities, cancer extent, ECOG performance score, pandemic period based on case peaks ( < 06/2020, 06-12/2020, 01-07/2021), and COVID-19 severity (death/hospitalization/ICU admission/mechanical ventilation). Results: Breast cancer patients (n = 804) with SARS-CoV-2 were mostly aged 50 years and above (75%) and urban residents (83%). The racial/ethnic makeup of the sample included: 13.3% non-Hispanic Black/African American (NH-Black), 11.7% Hispanic/Latinx, 4.9% American Indian/Alaskan Native (NH-AI/AN), 4.6% NH-Asian, and 65% NH-White. At SARS-CoV-2 diagnosis, 736 patients (91%) were scheduled to receive drug-based therapy (78%), radiation therapy (8%), or surgery (6%), of whom 39% experienced TDD. Across treatment modalities, the most commonly reported TDD reason from the clinic perspective was the patient’s COVID-19 disease (̃90%). Overall, NH-Black (62%), Hispanic/Latinx (44%), and NH-Asian (42%) adults with breast cancer and SARS-CoV-2 were more likely to experience TDD versus NH-White adults (34%) (p < 0.001). In multivariable analyses, NH-Black cancer patients were more likely to experience TDD compared to NH-White patients (aOR: 3.12, 95% CI: 1.96-5.47). The data suggest Hispanic/Latinx (aOR: 1.34, 95% CI: 0.78-2.30) breast cancer patients may also experience TDD, although not statistically significant. No association was observed among NH-Asian (aOR: 1.16, 95% CI: 0.50-2.73) or NH-AI/AN (aOR: 0.64, 95% CI: 0.28-1.52) breast cancer patients with TDD. Conclusions: Black or African American breast cancer patients are more likely to experience cancer care disruptions during the pandemic. Future research should evaluate the long-term impacts of care disruptions on breast cancer outcomes among minoritized US communities.