Talks to avert a 24 hour walkout on the tube starting on Sunday by London Underground (LU) staff resumed on Friday morning.
Negotiations between union chiefs and tube bosses were deadlocked on Thursday, just days before the strike, which threatens to bring the capital to a standstill.
All parties will get back round the table at government conciliation service ACAS on Friday.
TSSA and RMT union members are due to strike from 6pm on Sunday in a long-running dispute over job losses and ticket office closures.
Speaking on Thursday, RMT leader Mick Cash confirmed the talks had broken up "without any significant moves towards a resolution".
"We will be back again tomorrow [Friday] and we expect LU to come back with a radically improved package that fully covers the issues of jobs and safety at the heart of this dispute.
"Meanwhile, final preparations for the planned industrial action from Sunday night are now in place and our members remain determined to secure a just settlement that protects services and safety across the Tube network."
Manuel Cortes, TSSA general secretary, added: "Our negotiating team remains available for further talks throughout the weekend should they become necessary.
"However, our 24-hour strike action on the Tube remains scheduled to begin at 6pm this Sunday."
The strike is expected to hit the majority of tube stations in Zone 1, with Transport for London warning passengers to expect a "severely reduced service".
LU chief operating officer Steve Griffths claimed Transport for London was committed to working with unions to review staffing and reassign station staff roles where necessary.
"We have always committed to reviewing our new staffing model with our trade unions during its first year," he said.
"Following the review by London TravelWatch, we established a joint working group to undertake that review and make any changes necessary.
"It is clear that some more staff for stations are needed. We have started to recruit them and will continue to work with the unions to implement the recommendations made in the review.
"We believe that this will help us to provide a better service for our customers and ensure that they continue to feel safe, secure and able to access the right help while using our network.
"We encourage the trade unions to continue working with us in order to resolve this dispute and deliver the customer service our customers expect."
Keep up to date with the latest news in west London via the free getwestlondon app.
You can even set it to receive push notifications for all the breaking news in your area.