Commuters travelling to London are facing long delays today and tomorrow as RMT staff go on strike.
The 48-hour walk-out will affect London's tube network until late on Wednesday.
The action is being taken over plans to to close manned ticket offices at stations in the capital.
For more information on the strike, click here.
Station staff working for the rail operator Greater Anglia have voted to go on strike in a row over flexible working.
Members of the Rail Maritime and Transport Union on the West Anglia route backed a campaign of industrial action.
The union has about 100 members involved in the dispute. Its General Secretary Bob Crow has accused Greater Anglia of ignoring agreed procedures.