Almost 4,000 Amazon employees were mistakenly told to isolate by NHS Test and Trace.
The tracing programme told 3,853 staff members on Saturday that they were positive and must isolate, despite having tested negative, according to the Department for Health and Social Care.
Amazon has used PCR tests for its workers since autumn last year, and the online retailer reports results to Public Health England each day.
A spokesman for the Department of Health and Social Care said: "On Saturday, some Amazon staff members who tested negative for COVID-19 received notifications from NHS Test and Trace to say they have tested positive and asking them to self-isolate.
"Working closely with Amazon, NHS Test and Trace rapidly notified affected employees to let them know they did not need to isolate."
The spokesman added: "NHS Test and Trace has the capacity to process over 700,000 tests a day from more than 800 test centres and mobile units, with the vast majority of people reporting no issues with the process."
A spokesman for Amazon said: "We've communicated with our associates and partners to support them with the appropriate action steps, as instructed by the NHS."
No members of staff who tested positive were told they were negative.