London Underground workers are set to strike for two days as they continue to push for better contract terms and working conditions.
Trade union Aslef said its workers will stage two 24 hour walkouts on April 8 and May 4, the latter being the Saturday as the Mayday bank holiday weekend.
Finn Brennan, the union's organiser for the London Tube, said employers had failed to provide assurances about changes to conditions and terms.
He added: "Despite a previous commitment to withdraw plans for massive changes to drivers’ working conditions, London Underground management has established a full-time team of managers preparing to impose their plans.
"They want drivers to work longer shifts, spending up to 25pc more time in the cab, and to remove all current working agreements in the name of flexibility and efficiency.
"Everyone knows what these management buzz words really mean. It’s about getting people to work harder and longer for less."
Tube workers went on strike over the same issue a year ago.