A strike by some London Underground train drivers will go ahead after talks failed to resolve a dispute.
The talks between the Rail, Maritime and Transport union (RMT) and Transport for London (TfL) continued for hours on Monday but no resolution was found.
Here's everything you need to know.
When are the strikes?
RMT members will walk out on Tuesday and Thursday which will lead to heavy disruption across the network.
On both days, there will be a limited service before 6.30am and customers have been urged to complete their journeys by 9pm.
A normal service is expected on Wednesday and Friday.
Which lines are affected?
TfL said no service is expected on the Circle line, Piccadilly line, Metropolitan line between Baker Street and Aldgate and the Central line between White City and Liverpool Street.
Services are expected across all other Tube lines on both days, but disruption to journeys is expected with service levels varying across the network.
Heathrow Airport said on X that rail replacement buses will replace the Piccadilly line at affected times, with all other services, including the Heathrow Express and bus services, running as normal.
How do you avoid them?
TfL advises travellers to plan ahead and check before you travel by using its TfL Go app, which helps people to find how to get from one point in London to another by public transport, Journey Planner (a web-based service), or by using the latest status updates on the TfL website.
Why are they happening?
The RMT union is opposed to a new, four-day week because of the impact on length of shifts and other "critical" issues.
But TfL stressed the proposals are voluntary and branded the decision "bitterly disappointing".
ACAS, a conciliation service, was involved in the talks.
An RMT spokesperson said: "Despite our best efforts in ACAS talks, TfL have failed to provide assurances on our members' deeply held concerns around fatigue, reduced flexibility, shift lengths and the impact these proposals could have in a safety-critical role like Tube driving.
"We remain available for meaningful talks, but strike action tomorrow will now go ahead."
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A TfL spokesperson said: "It is bitterly disappointing that despite five hours of meetings with the RMT at Acas and repeated assurances that the four-day working week proposals will remain voluntary, RMT has chosen to continue with its disruptive strike action.
"We will do all we can to provide as much service as possible during this action."
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