Commuters are facing strike action on two Tube lines later this week.
Members of the Rail, Maritime and Transport Union have planned to stage a 24-hour walk-out on the Circle and Hammersmith and City lines from 9.30pm tomorrow.
If the drivers' walkout goes ahead there will be no Hammersmith and City Line services at all from 9pm tomorrow and all day on Friday, transport bosses said.
Out of the 265 drivers on the Circle and Hammersmith & City lines, eighty two RMT members were balloted. Fifty took part in the vote and 43 voted to go on strike.
"Very limited Circle Line services will run but TfL have warned passengers that trains will be much less frequent than usual and extremely busy, especially at peak times.
Services may also be subject to last-minute cancellations.
London Underground are involved in urgent talks to have the strke called off. The walkout is over what TfL calls "local-level issues" at two out of three depots covering the lines.
Services on other Tube and Rail lines, the bus network and river services will run as normal but are expected to be busier as passengers seek alternative routes.
Some roads in west and central London could also be busier than usual.
Customers are advised to allow more time for their journeys.
Steve White, Operations Director for London Underground, said: "We are speaking to the RMT union to try to resolve the issues without disruption to our customers.
But if the strike does go ahead, customers are advised to check our real-time travel information.
"All other Tube lines and other TfL services will be operating as normal and well be making sure that everyone has the information they need to re-plan their journeys if necessary.
Planned weekend engineering works mean there will be no Circle or Hammersmith & City line service between Hammersmith and Edgware Road only on September 17 and 18.
