Medibank Private's 3.8 million customers may not be able to submit their tax on time as the health insurer flags a glitch.
Most private insurance holders need a statement for tax time each year to avoid paying the Medicare levy surcharge, but Medibank Private chief executive Craig Drummond said theirs may not be ready in time.
"I sincerely apologise to our customers for this disruption," Drummond said in a statement.
"Our team is working around the clock to resolve this issue, and I want to assure customers that our focus is on minimising the impact this will have on them."
Drummond said the customer database was affected in a botched technology upgrade. Tax submission need to be submitted by the end of October.