Thousands of London Underground staff, including drivers, have voted to go on strike - and action could be taken in the run-up to Christmas.
The Rail, Maritime and Transport (RMT) union said station and platform staff backed walkouts by 85% over staffing and safety.
Meanwhile, a similar number of union members working as drivers on the Tube's Piccadilly Line have also decided to support industrial action - that's thanks to a "wholesale breakdown" in industrial relations.
FYI, around 3,400 workers are involved.
The news followed an announcement from the Transport Salaried Staffs' Association (TSSA) that it will ballot hundreds of its Tube members for strikes over the closure of ticket offices.
The two unions could now co-ordinate any action in the run-up to Christmas.
The RMT executive will consider the ballot results before deciding the next move.
General secretary Mick Cash said: "RMT members on the London Underground stations see day in and day out the toxic impact of the job cuts programme and they are reporting back that it is horrific.
"With the constant overcrowding on stations and platforms it is only a matter of time before there is a major tragedy if we don't act decisively. Our dispute is about taking action to haul back the cuts machine and put safety back at the top of the agenda.
"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 TSSA said its members had been subjected to increased threats and abuse since a programme of ticket office closures started.
A survey for the TSSA found that most of the 540 staff felt less safe since they moved from ticket offices on to station concourses.
The so-called Fit for the Future programme was introduced by former London mayor Boris Johnson. His successor Sadiq Khan has ordered a review of the ticket office closures.
TSSA leader Manuel Cortes said: "My members say Fit for the Future working practices are fit for nothing and should be scrapped.
"They are overstretched by the rosters, stressed by how unsafe the Tube has become, and fed up with the spikes in abuse, both verbal and physical, from passengers."
The union said staff were being targeted by frustrated passengers if ticket machines do not work.
Steve Griffiths, Transport for London's chief operating officer for London Underground, said: "Our staff work hard to serve the millions of customers that pass through the Tube and rail network every day.
"Everyone has the right to go about their work without fear or intimidation and we do not tolerate any form of verbal or physical assault on our staff."