Plans to launch an all-night Tube service in London on September 12 have been deferred.
London Underground said it wanted to allow more time for talks with unions to reach a deal on pay and conditions for the new service.
No new date has been announced, but LU said it wanted an agreement to help launch the night Tubes in the autumn.
Rail unions have staged two 24-hour strikes in a dispute over the new service and had threatened longer walkouts this week before suspending the action.
London's Mayor Boris Johnson has said he "wasn't fussed" about a launch date, as long as night Tubes started in the autumn.
LU said practical arrangements were now in place, but talks with unions on rosters were continuing, so it was not possible to meet the September 12 date.
The company said it was "deferring" the launch to allow a successful conclusion of talks.
LU managing director Nick Brown said: "Further to the progress made in recent days with the trade unions and the suspension of strike action, we believe we are not far from an agreement that protects the work-life balance of our employees and is affordable, sustainable and fair.
"As such, we have decided to defer the introduction of the night Tube to allow more time for those talks to conclude. Our objective is to reach an agreement that ends this dispute and delivers the night Tube for Londoners this autumn."
24-hour Tube service
Mick Whelan, general secretary of the drivers' union Aslef, said: "We welcome this decision by London Underground, which gives us all the time and space to negotiate properly on the introduction of the night Tube in the capital.
"Aslef believes that a world-class capital city like London needs a 24-hour Tube service, but not at the expense of the work-life balance of our members. It has to be done in a way that works for London Underground, for passengers, and also for the drivers who deliver this service every day.
"Had LU not acted in bad faith, by trying to introduce the night Tube in London without consultation, and without negotiation, we wouldn't be where we are today and they would have been in a position to deliver. Common sense has broken out at London Underground and now we can sit down with them and work this out."
David Leam, of business group London First, said: "This is disappointing for businesses, but if it gives London Underground and the unions time to come up with a long-term deal it will be worth it.
"It's high time we have a transport system that means London is truly a 24/7 city, as places like New York have been for years."