Drivers on the Piccadilly line plan to strike from 9pm on Wednesday 23 March for 24 hours.
The RMT union says there's been "a prolonged period of industrial problems" — some of which it lays at the feet of the "ageing Piccadilly line fleet". The line has experienced a number of problems recently, including delays because of up to 17 trains being out of action and a door opening on a moving train. The union also accuses management of harassing and threatening staff.
Transport for London expects there to be no service on the line from around 10.30pm on Wednesday and warns that interchange stations like King's Cross, Finsbury Park and Green Park will be busier than usual.
There are more Piccadilly line strikes planned for the week of 18 April. We'll keep you posted.