London could be hit with more travel chaos in February if the Underground station staff dispute is not resolved, the RMT Union warned on Thursday (12 January).
The threat comes after a 24-hour walkout of RMT and TSSA Union members on Sunday 8 January saw a majority of Zone 1 stations being closed.
The RMT's ruling body, its national executive, agreed to call escalated strike action from Monday 6 February unless the union's demands are met.
"It has now also been shown that at management level there is agreement with the union that the cuts have been a disastrous mistake and that the staff need to be put back on the stations," said Mick Cash, the general secretary of the RMT.
"We now need a move away from the piecemeal and incremental approach to tackling this crisis and for LU to come forward with a serious package of proposals.
"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."
Cash said the union's overtime ban of station staff will remain in place. The dispute is over former Mayor of London Boris Johnson's Fit for Future stations programme, which saw more than 800 jobs cut.
Underground bosses have agreed to hire more staff to man stations, but the unions want a bigger recruitment drive.
The TSSA said it is in negotiations with senior Transport for London (TfL) on Thursday, while further talks with the union, the RMT and management are scheduled at mitigation service Acas on 16 January.
Steve Griffiths, London Underground's chief operating officer, said: "We look forward to resuming talks at ACAS on Monday in order to make progress towards resolving this dispute."
Labour's Mayor of London Sadiq Khan, who was backed by the TSSA in his City Hall campaign, had promised voters that his time in office would be strike-free. He described the walkout in January as "unnecessary".
"We've made huge progress on addressing this dispute, which began under Boris Johnson, and we are committed to resolving it amicably," he said.
"A good deal, that will ensure station safety and staffing levels across the Tube network, remains on offer, and I urge the unions to continue talks. Londoners deserve a resolution to this without any further industrial action."