Hundreds of London Underground drivers are to stage a 24-hour strike next month in two separate disputes.
The strikes will coincide with another walkout by guards on Southern Rail.
Members of the Rail, Maritime and Transport (RMT) union on the Piccadilly and Hammersmith & City lines will walk out from 9.30pm on Tuesday December 6 over claims of a breakdown in industrial relations, breaches of procedures and bullying and harassment of staff.
The Piccadilly line is one of the busiest on the London Underground network and serves Heathrow Airport.
The stoppage will coincide with a two-day strike on December 6 and 7 by RMT members on Southern Railway in the long-running row over changes to the role of conductors.
RMT general secretary Mick Cash said: "The dispute on the Hammersmith & 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."
Steve Griffiths, London Underground's chief operating officer, said: "We urge the RMT leadership to work with us constructively on the issues it has raised rather than disrupt our customers with strikes.
"The announcement of strike dates is premature given that we have pre-arranged talks planned at Acas tomorrow to discuss the RMT's concerns on the Piccadilly line, and on the Hammersmith & City line we are waiting for the RMT's response to our proposals to end that dispute."