Two Tube strikes are planned for this week and look likely to cause four days of travel disruption for commuters.
Last-ditch talks aimed at averting the action are taking place - but here's everything you need to know should the strikes go ahead.
When do the strikes start?
London Underground workers are staging two 24-hour walkouts - the first starting at 18:30 BST on Tuesday and another from 18:30 on Thursday.
Station staff will walk out from 18:30 on each of those days and drivers from 21:00 - but TfL says services will stop running from about 18:30.
And even though the strikes are supposed to be 24 hours each, it's likely services will be affected from Tuesday evening right through to the end of Friday.
So what's the day-by-day rundown?
- Tuesday: Services will be exceptionally busy between 16:30 and 18:30 - so aim to get where you need to be before then. Services will stop completely from 18:30, says TfL
- Wednesday: Most Tube services are unlikely to run at all and those that do will be less frequent than normal
- Thursday: Tube services are planned to start at the usual time but there may be lasting impact from the night before. Services will stop completely from 18:30, so again, complete any journeys well before then
- Friday: The same story as Wednesday - most Tube services are unlikely to run at all and those that do will be less frequent
- Saturday: Tube services should be back to normal
Are any lines running?
Transport for London (TfL) says it will "run whatever Tube services we can" based on the number of staff who turn up for shifts.
Most lines are expected to be closed, and those running at all are likely to only serve certain stations, and only run for part of the day.
London Overground, DLR, Transport for London Rail and trams will all operate a normal service - but will be exceptionally busy at peak times.
How should I travel?
Walking could be your best bet.
Below is a walking map of central London showing the walking time, in minutes, between stops.
But arm yourself with a brolly/wellies/waterproofs - the forecast is wet (though fortunately with some sunny spells).
Or if you're looking for an excuse to keep fit, here's a calorie-burning map of the city.
Any other options?
But, a word of caution, during the last strike buses were delayed by up to an hour, particularly in zones one and two, says TfL. And don't forget buses don't accept cash.
Extra river services are running, and extra bikes are available to hire, along with extra cycle hubs (full list here).
The Emirates Air Line cable car is also open until midnight on Thursday - Oyster and travelcards will be accepted.
If driving, be aware the congestion charge remains in place from 07:00 to 18:00 and roads are likely to be very, very busy. But some road works are being suspended to help traffic flow.
If travelling by road or river it's essential to check the latest before you travel - and try to make your journey outside rush hour.
And lastly, check rail services before travelling too as there are a few service disruptions planned.
And if all else fails?
- Work from home
- Car share with a neighbour
- Book a taxi - but leave plenty of extra time
- Take a bottle of water, some comfy shoes and a good book (or podcast, playlist or iPlayer episode) and be prepared for a wait...
What about getting to airports?
Getting to Heathrow is likely to be difficult, as the Piccadilly line is not running.
But Heathrow Express services from Paddington are operating, and rail services to Gatwick, Luton and Stansted airports are running.
Again, services are likely to be busy, so leave more time and check the latest updates.
So is this action linked to the last lot?
Yes, it's part of the same dispute.
The latest strike was called after talks failed to resolve a dispute between unions and London Underground over plans to bring in all-night Tube services.
Members of the Rail, Maritime and Transport union (RMT), Transport Salaried Staffs Association (TSSA) and Unite are involved in the strike. But Aslef, whose members took part in the previous action, has decided not to participate this time.
When will it all end?
The strike is due to end at 18:30 BST on Friday - but it's likely disruption will continue into the night.
Normal services are not expected to resume until Saturday...
Can I get a refund if I've already bought a ticket?
The short answer is no.
This is because TfL says strike action is beyond its control so no refunds will be offered.
But printed single Tube tickets will be accepted on bus and tram services on "reasonable" alternative routes, though not on National Rail services.