The first of two co-ordinated strikes which looked likely to bring major disruption on the Tube is in doubt, after one union said it would pull out.
The dual strike looked certain to close much of the Tube
Aslef, which represents about 70% of Tube drivers, says it will recommend the 21 February strike is suspended, after talks with London Underground.
It said progress was made on several issues in the industrial relations row, but not enough to end it altogether.
The other union involved, the RMT, will hold talks with LU on Wednesday.
An Aslef spokesman said on Tuesday: "Progress has been made on a number of issues that have been identified.
"However there are issues that still require resolution for Aslef to call off the dispute in its entirety.
Aslef Executive Committee Member for London Underground Terry Wilkinson added they intended to recommend the 24-hour walkout next Tuesday, "to allow talks to progress further".
Two walkouts were planned by both unions, which together represent about 3,500 drivers, after they accused LU of a "breakdown in industrial relations". Another strike is due on 2 March.
'Regime of fear'
The row covers various issues from LU's policy on signals passed at danger (Spads), to health and safety, alleged harassment and bargaining arrangements.
On Tuesday the Rail, Maritime and Transport union (RMT) suggested in a letter that LU managers were imposing a "regime of fear" on staff.
RMT leader Bob Crow said there was a "growing sense that the aim is somehow to 'break' the unions".
In response LU said it remained ready to meet the unions at any time and was consulting on new harassment, disciplinary and attendance procedures.
"If any employee or union has a genuine grievance, the only way to resolve it is through discussion using the procedures agreed by unions and management," a spokesman said.