Last-ditch talks will be held today to resolve a dispute over plans to privatise the work of health staff who drive patients to and from hospitals.
Staff employed by the London Ambulance Service voted in favour of strikes and the GMB warned action will go ahead unless the talks are successful.
The work of transporting patients across south east London was put out to tender by South London Healthcare Trust.
GMB official Rob Macey said: “GMB members have now voted in an official ballot for strike action to prevent Savoy Ventures being awarded this contract and to get cast-iron assurances that the rules on procurement and staff transfers will be adhered to.
“The talks are now crucial to avert strike action. If there is no satisfactory outcome from the talks, the strikes will go ahead.”