Transport for London is asking commuters to avoid its services as thousands of union members gear up to go on strike.
Those responsible for running travel across the capital say its customers should expect 'severe disruption' this week.
Unless absolute necessary travellers are being asked to completely avoid using TfL services, including the London Underground, on Tuesday and before mid-morning on Wednesday because thousands of London Underground workers are walking out.
Their industrial action is coinciding with the first of three national rail strikes that also begins on Tuesday at just after midnight and will last for 24 hours.
More than 30,000 RMT members across Network Rail and 13 train operating companies are planning on three separate 24-hour strikes on Tuesday, Thursday and Saturday in a dispute over jobs and pay.
If customers cannot avoid travelling tomorrow (Tuesday), says TfL, then people must plan ahead and leave more time to travel while all journeys should be completed by 6pm with Elizabeth Line customers travelling between Paddington and Reading, and Shenfield and Liverpool Street advised to complete their journeys by 4pm.
While an enhanced bus service will run during the strike period, say planners, it will be busy with long queues expected and so customers are being asked to walk or cycle if they can.
Andy Lord, TfL’s Chief Operating Officer, said: "I want to apologise to our customers for the impact these strikes will have on their journeys and urge people to avoid travel on all TfL services on June 21 unless absolutely necessary. If they are travelling, they must complete journeys by 18:00, and expect disruption across the network. Walking and cycling is likely to be the best way to get around during this action.
"The strike on the London Underground has been timed by the RMT and Unite unions to cause maximum disruption to our millions of customers by coinciding with strike action on national rail services.
"Additional strikes on national rail services next week will also have an impact on London Underground, Overground and Elizabeth line services because of shared track and assets. TfL customers are therefore advised to plan ahead and leave more time for their journeys."
Here's how services are set to be affected by strike action this week:
Tuesday, June 21
With London Underground and national rail strikes happening on Tuesday all services will be hugely disrupted. There is likely to be severe disruption or no service at all on all London Underground lines on Tuesday.
The Elizabeth line will be running a reduced service. Services between Paddington and Abbey Wood will be running a reduced service between 7am and 6pm and customers are urged to complete their journeys by 6pm. The west (Paddington to Reading and Heathrow) branches of the Elizabeth line will run a reduced service from 7.40am and on the east (Liverpool Street to Shenfield) from 7.30am, with customers on these branches advised to complete all journeys by 4pm.
The London Overground will run a reduced service between 7.30am and 6pm, services running are expected to be very busy and may not be able to stop at all stations is the warning.
While other TfL services are running on Tuesday they are likely to be busy - with customers using DLR services from stations also served by London Underground advised to check before they travel due to possible station closures for safety reasons.
Santander Cycles will be available, with teams ensuring bikes are distributed at key locations according to demand, promises TfL, while rental e-scooters are also available to hire in some London boroughs.
Wednesday, June 22
There will be no London Underground services running before 8am on Wednesday and a reduced service on the London Overground and Elizabeth line.
Customers should avoid services before mid-morning, is the request from TfL.
Thursday, June 23 and Saturday, June 25
National rail strikes are running on both these days.
There will be a reduced service on the London Overground and Elizabeth line on these days due to the national rail strike and its impact on shared track and assets. Services running are expected to be very busy and may not be able to stop at all stations.
The central section of the Elizabeth line will still be running a reduced service but will close as normal at 11pm. The London Overground will run a reduced service between 7.30am until 6pm.
There will be no service from Queen’s Park to Harrow & Wealdstone on the Bakerloo line and on the Richmond and Wimbledon branches of the District line services will only operate between 7.30am and 6.30pm.
The Waterloo & City line will operate as usual on Thursday but has a planned closure on Saturday, June 25.
There is also the potential for disruption due to the strike impacting London Underground staff availability, meaning customers should still check before they travel.
Friday, June 24 and Sunday, June 26
Disruption from the national rail strike will affect customers on mornings even when no strike action is planned, expects TfL.
London Underground customers using sections of the Bakerloo and District lines, which will be affected by national rail strike action, are encouraged to avoid making journeys until mid-morning.
Elizabeth line and Overground services will start later than usual so the advice here is to also check before travelling.