Train drivers' union Aslef has warned strike action could still be brought to the London Underground, despite suspending a 24-hour walkout planned for Thursday 5 October.
Asflef's organiser on the London Underground, Finn Brennan, said: "Our ballot remains live and we will not hesitate to call action in the future if needed to ensure all the commitments are fully delivered."
Read more: This week's Tube strike has been called off
The strike planned over working conditions was called off yesterday after the union said "sufficient progress" was made in talks with Transport for London to suspend action. But Aslef warned it "has, and always will, insist that management stick to agreements they make with us".
It comes as a separate dispute over the role of the guard has spread to another train operator, with strikes over the issue planned tomorrow across Southern rail, Merseyrail, Arrival Rail North and Greater Anglia after a walkout yesterday.
The Rail, Maritime and Transport (RMT) union announced yesterday that workers on South Western Railway had now voted in favour of strike action too, meaning five train companies could soon be embroiled in industrial action.
The new railway franchise is now called South Western Railway and replaces South West Trains, operating across London and the south of England. FirstGroup and Hong Kong company MTR took over the franchise on 20 August.
The union said it had failed to secure guarantees from the firm over the future role of the guards, while SWR has said the dispute is unnecessary, as it planned to bring more drivers and guards onto its trains.
And today, the RMT ramped up its row with Southern rail, which has been underway for over a year, saying the firm had made a threat over staff pensions.
"Instead of resorting to the gutter tactics of the playground bully, Southern should start acting responsibly and should get round the table with the trade union for serious talks aimed at resolving the longest-running industrial dispute in Britain," said the union's general secretary, Mick Cash.
A spokesman for Southern said: "We reject the latest claims made by the RMT. Tomorrow will be the 36th day of RMT strikes and we, like our passengers and the vast majority of our colleagues, simply want an end to this unnecessary dispute."
Paul Plummer, chief executive of the Rail Delivery Group, which represents train operators, said: “Passengers, communities and Britain want rail companies working together to deliver a long-term plan to improve services, not needless and opportunistic attempts to disrupt lives and the economy."
He added that the RMT leadership should "work in the interests of the nation and resolve these disputes".
Tomorrow's rail strikes:
Arriva Rail North - said it will run around 1,200 services a day, just under half of its normal timetable
Greater Anglia - said it will run a full service after making contingency arrangements
Southern - said it will try to run a normal service on most of its routes, but a service will operate on the West London line at peak times only
Merseyrail - said it will be running a reduced service across the majority of its network, adding that most trains will run every half hour from 7am to 7pm with a break between 11am to 2pm