Fresh talks will be held today in a bid to resolve a bitter row over new all night underground services in London, which has led to strike action over the past month.
Members of four unions walked out for the second time last week, closing down the Tube system, causing travel chaos.
The conciliation service Acas will chair the talks, with Tube travellers hoping the deadlock will be broken.
Unions are likely to call more strikes, possibly for 48 hours, unless there is a deal.
Workers are unhappy with shift arrangements for the all night Tubes, which are due to start on September 12.