London Underground passengers face disruption in the lead up to Christmas as fresh industrial action has been announced by train drivers.
The RMT union said two strikes would be taken by Central Line workers on 21 and 22 December.
Transport for London (TfL) said the row was over a driver who was sacked for failing a drugs test before a shift.
But the RMT’s general secretary said relations with TfL were at “breaking point”.
It follows strike action on 7 November which closed the Central and Waterloo and City Lines.
Drivers will walk out for six hours from 08:00 GMT on 21 December and for 16 hours from 04:00 on 22 December.
The union accused London Underground of “refusing to lift a finger” to resolve a series of issues, claiming not enough drivers were employed and a union member had been victimised.
London Underground’s Nick Dent described the strikes as “unjustified”.
He added: “They are demanding the reinstatement of a driver who was sacked for failing a drugs test, something for which we have zero tolerance.”