The Royal Mail has asked customers to steer clear of using red envelopes for Christmas cards.
Workers at the sorting office in Slindon Street, Portsmouth, say they can cause problems with the scanning machines, making the sorting process longer.
Lynne Bloor, advanced customer service advisor said: ‘The orange code printed on the envelopes for sorting becomes almost invisible to see, so the cards have to be manually sorted.’
But the Royal Mail says it can find a way around.
She said: ‘Most Christmas cards have red envelopes, so we know that we cannot escape the problem entirely.’
The Royal Mail has instead asked customers who still wish to use a red envelope to place the address on a white sticker, and not to write in a blue pen as it becomes difficult to read on the red background.
Ms Bloor added: ‘The cards will still arrive on time as we dedicate our time to providing that service.
‘In all honesty, we have more trouble with people who do not address their envelopes properly.’
Royal Mail also want to remind customers of the last posting dates before the Christmas period.
First class is December 20 and special recorded delivery, December 23.