Independent contractors who deliver Amazon packages in their own vehicles were told that some may not be paid on time due to this week's Amazon Web Services outage.

The app Flex drivers use to choose shifts, see route deliveries, and check earnings is also continuing to experience glitches, the company said.

The outage also impacted Amazon's warehouse workers, with many offered unpaid time off as systems ground to a halt.

In an email seen by Business Insider, Amazon told Flex drivers that "a small portion of delivery partners may have a payment delay until December 14." It is not clear how many of the drivers will have a late payment.

During the outage itself, the cause of which is disputed, the Flex app was down entirely, making it hard for drivers to know if they should turn up to delivery stations, or see a record of package deliveries.

Tips were also not always visible, but Amazon said that all tips would reach drivers.

The company this February reached a $61.7 million settlement with the Federal Trade Commission for illegally withholding tips to more than 140,000 Amazon contract drivers.