Thousands of London Underground staff began a series of strikes Sunday that threaten to halt service on the subway system used by millions of people every day.

The Rail, Maritime and Transport union, known as the RMT, said its members — including drivers, signalers and maintenance workers — will walk out at various times through Thursday. Transport for London, which operates the Underground, said services were severely disrupted Sunday and that there are expected to be few or no trains running from Monday through Thursday.

TfL said it has offered staff a 3.4% pay increase but the union is holding out for a reduction in the working week from 35 hours to 32 hours. TfL said it cannot afford the shorter working week. The RMT argues that staffing on the Underground has fallen by about 2,000 since 2018 and that members are coping with "extreme shift patterns," placing additional strain on remaining employees.

No talks between the union and management were planned as of Sunday, the RMT said, and the union called on London Mayor Sadiq Khan to intervene to end the dispute. TfL did not announce immediate plans for fresh negotiations.

The strike marks the latest episode in a series of labor disputes affecting Britain's transport sector amid long-running disagreements over pay, staffing levels and working conditions. The Underground carries millions of passengers daily and is a backbone of London's public transport network; extended stoppages are likely to cause significant disruption to commuters, businesses and visitors.

Transport operators and city officials typically advise passengers to plan for alternative travel arrangements during strikes and to check service updates before travelling. On Sunday, TfL urged customers to avoid travel on the Tube where possible and to allow extra time for journeys, while bus and surface services remained subject to separate operational pressures.

The RMT's demand for a cut in the contracted working week reflects wider debates in the labor movement about workload and work–life balance, while TfL's reference to affordability underscores the financial constraints facing the transport authority. TfL's finances have been a matter of public and political scrutiny in recent years, affecting its capacity to meet unions' demands without additional funding or adjustments to service budgets.

As the strike action continues through Thursday, passengers and employers in London are preparing for prolonged disruption. Both sides have so far given limited indication of movement toward a resolution, leaving the scale and duration of the impact dependent on whether negotiations resume or new offers are tabled.