Commuters are facing fresh strikes on the Southern and Gatwick Express lines in a row over driver-only trains.
Drivers have voted overwhelmingly in favour of industrial action on the two franchises, which are both operated by Govia Thameslink.
The train services – which include busy commuter routes into Victoria – have already faced strike action from conductors in recent weeks over the plans to introduce driver-only trains.
The Aslef union said drivers at the two railway services backed walkouts by 84 per cent and other forms of action by 95 per cent, on a turnout of 82 per cent.
General secretary Mick Whelan said he welcomed the "strong mandate" from drivers.
Govia Thameslink expressed disappointment at the Aslef ballot result and confirmed it was seeking an injunction against any industrial action.
A spokesman said: “We are disappointed with the result and will now await notification from Aslef as to what its plans may be.
“Any action would only heap more disruption on our passengers - passengers who have already been through two recent strikes by RMT union conductors.”
They added: "We have sought an injunction from the High Court against any industrial action that may result from this ballot.
“Aslef selected which drivers it balloted in a way that breaches the strict rules on balloting, and because it induced drivers to refuse to drive trains in advance of conducting the ballot, it cannot now lawfully ask them to take industrial action.”
The company said the case will be heard on Tuesday.
Additional reporting by the Press Association.
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