The threat of more strikes on the Tube has been raised after talks to try to resolve a long-running pay dispute ended without agreement.
Strikes last year crippled the Tube network
London Underground (LU) managers and leaders of two rail unions have spent two days at the conciliation service ACAS trying to reach a deal on a dispute which prompted two strikes last year.
The unions were offered an extra 0.75% on top of a rise of 3% imposed last year.
But they wanted at least an extra 1% as well as a shorter working week, pension improvements and better travel facilities.
The 24-hour strikes by the Rail Maritime and Transport union (RMT) and Aslef paralysed the Tube in September and October last year.
RMT general secretary Bob Crow said there would be industrial action again if the dispute was not settled.
"We are serving notice on London Underground that we want these issues addressed now", he said.
London mayor Ken Livingstone stepped into the dispute in October and promised to take it to non-binding mediation when he took over the running of LU.
Mr Livingstone's Transport for London (TfL) took over the Tube last month and now has control over how the network is managed and run.
The mayor said he hoped to agree a three-year pay deal with Tube workers to end the damaging strikes.
But talks on that cannot begin until the current pay dispute is settled.
"There has been no recognition of the huge cost of living in London, so how can there be any talk of three-year deals?" Mr Crow said.
"We were told there would be a new order on London Underground following the transfer of the Tube but all we have seen so far is the same meat with different gravy."
Mike Brown, LU's chief operating officer said: "The new Tube management team is now looking forward to moving towards a multi-year stability agreement, covering pay and conditions.
"We believe that is what management, Tube passengers and staff all seek."
The pay negotiations at ACAS covered about 11,000 Tube workers, including all drivers, station and signalling staff and some administrative staff.
The new LU management team is in charge of day-to-day operations and staffing of stations, while two infrastructure companies (Infracos) are responsible for maintenance and modernisation for the next 30 years.