Drivers on a major train route serving London and the south of England have voted overwhelmingly to strike over plans to introduce driver-only trains.
The motion for more industrial action against GTR Southern and Gatwick Express was carried with a majority of 4-1 to over plans to make drivers close train doors - which is normally done by guards on the station platforms.
In a statement, Aslef said: "Mick Whelan, general secretary, has welcomed the strong mandate from GTR Southern & Gatwick Express members who have voted overwhelmingly in favour of taking action over the dispute concerning the extension of driver only operations.
"95.8% of our members voted Yes to taking part in industrial action short of a strike and 84.4% voted Yes to taking part in a strike, on a turnout of just over 82%".
Guards are also said to be considering more industrial action after two previous strikes.
The Rail, Maritime and Transport union later announced that its train driver members at Southern and Gatwick Express have also voted for strike action and action short of a strike in the same dispute.
The RMT is embroiled in a row with Southern over the role of conductors, which has led to strike action in recent weeks.
Unions are also protesting against parent company Govia's plans to close over 80 ticket offices across its franchises.
The company expressed disappointment at the ballot result and confirmed it would press ahead with seeking an injunction against the strike.
A spokesman for Southern 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.
"We have repeatedly tried to engage with Aslef on this but the union has refused to engage in any sort of meaningful dialogue. We urge them once more to sit down and talk to us.
"In the meantime, 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 that, 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 has said the move will free up the guards to help passengers on the station but Aslef and RMT say it is unsafe.
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