Hundreds of London Underground drivers are to stage a 24-hour strike over December 6/7 in two separate disputes.
The strike will coincide with another walkout by guards on Southern Rail, the RMT union announced.
The lines affected will be the Piccadilly and Hammersmith and City Lines and the strikes will run between 21.30 on Tuesday 6 December and 21.29 on Wednesday 7 December.
The disputes are over industrial relations, breaches of procedures and bullying and harassment of staff.
The Piccadilly Line is the fourth busiest on the London Underground network and serves the terminals at Heathrow Airport.
The Southern Railway strike is over a long-running row regarding changes to the role of conductors.
RMT General Secretary Mick Cash said: “This dispute on the Hammersmith and City Line is about the basic issues of protecting working conditions of our members and defending agreements from attempts to drive a coach and horses through them. The management are out of control and the anger at their failure to follow procedures has boiled over.
”This breakdown in industrial relations should never have been allowed to happen and if agreements and processes had been adhered to from the off the package of issues at the heart of the dispute could have been resolved through the joint machinery.
“In the separate dispute involving drivers on the Piccadilly Line, safety is again a major factor and is tied in with the ripping up of policies and procedures and ignoring warnings from staff. Our members have been left exposed and vulnerable and we have no choice but to blow the whistle before lasting damage is done.
“The union remains available for talks in both disputes.”