City Hall staff were still in discussions with the Government over a multibillion-pound funding plan for the capital’s buses and Tubes on Thursday morning.
TfL accused the RMT union of “undermining” its bailout negotiations with further threats of strike action when talks on Wednesday failed to produce an agreement.
TfL’s director of people, Fiona Brunskill, said further walkouts could have “dire consequences”.
Tube staff, along with London Overground workers, have announced industrial action for August 19 — between national rail walkouts on August 18 and 20 — in a dispute over pay, pensions and jobs. It follows strikes in June and July, which put further strain on TfL’s finances.
The RMT said one of its main reasons for balloting members was City Hall’s refusal to share details of the Government funding deal and TfL failing to provide “assurances on pensions and working conditions”.
A short-term funding deal expired at midday on Wednesday, with TfL now using reserve cash to carry on.
Fears over the cost of industrial action and the settlements needed to appease unions are believed to be one of the sticking points in negotiations.
In a letter to RMT chief Mick Lynch, seen by the Standard, Ms Brunskill said further industrial action will “undermine our negotiations with Government”.
TfL got £5 billion during the pandemic, and says it needs at least £927 million for the rest of this year plus long-term funding.
“Our latest forecast shows that we currently have sufficient cash available to enable operations to continue,” a TfL spokesman said as
“However, our overall level of confidence of longer term support will be closely monitored and reviewed by the interim Chief Financial Officer on a regular basis.”
Mr Lynch said: “We are prepared to work with TfL, but our members will not be sacrificial lambs on the altar of austerity.
"Strike action is scheduled to go ahead on the August 19 and we remain open to finding a negotiated settlement."
A Department forTransport spokesman said: “Over the past two years, the Government has provided TfL with more than £5 billion worth of funding and ensured our capital’s transport system kept running throughout the pandemic.
“The latest deal we have offered would take this funding to over £6 billion, as well as supporting more than £3.6 billion worth of major projects – such as tube upgrades and extensions and new active travel schemes to allow for less congestion and pollution.
“It is clear we are committed to supporting London’s transport network, but this must only be done in a way that is fair and represents value for money for taxpayers across the country. This deal, which would transform the travel for millions of Londoners, remains on the table as we continue our discussions with TfL.”