Royal Mail workers are striking on multiple days across the next few months, with people warned to expect delays to their parcels and letters.
Around 115,000 staff are walking out over pay and conditions in what the Communication Workers' Union (CWU) says is the biggest national strike of any sector this year.
Twenty-one days will be affected by the strikes, which the union says will have a "dramatic impact" on peak periods such as Black Friday, Cyber Monday and the run-up to Christmas.
Royal Mail says it has "well-developed contingency plans" but "cannot fully replace the daily efforts of our frontline workforce".
Here's a day-by-day guide to the strikes.
13th, 20th, 25th October; 28th November
These are likely to be the days with the worst disruption as it involves delivery and collection staff, as well as those who sort parcels and letters.
Royal Mail says it's "doing what we can" to keep services running but customers are warned of "significant disruption".
No letters at all will be delivered (apart from Special Delivery).
Any items posted the day before, during, or in the days after these dates could be delayed.
Special Delivery mail will still be prioritised "as resources allow" but the usual next-day guarantees are being suspended and customers can't claim compensation for delays.
Tracked 24 mail, including medical prescription items and COVID tests, will also be prioritised but people are again warned to expect delays.
Delivery Offices and Customer Service Points will be closed.
Post Offices will stay open and offer their usual services but Royal Mail collections will be limited.
People can still drop mail at postboxes but there will be fewer collections and items face delays.
Significant disruption is still likely on the dates below, but as not all staff are involved Royal Mail says it will only affect "parts of our operation".
3rd, 9th, 15th, 24th November; 1st December
Processing, distribution, international, collections and admin workers go on strike.
Delivery staff are not yet involved on these days, so some people may still receive items.
4th, 10th, 16th, 25th November; 2nd December
These walkouts are currently set to only involve delivery workers, so collections from postboxes and Post Offices should take place.
2nd, 8th, 14th, 23rd, 30th November
"Network" staff walk out but delivery and collection staff should be working.
However, given the close proximity to the other strikes and a build-up of delayed mail, disruption is still very likely and people are advised to post items well in advance if possible.
"After industrial action takes place, we'll be increasing our network capacity and using additional resources to assist with getting services back to normal," says Royal Mail.