Train drivers' union Aslef has announced fresh strike dates for August, in a dispute with Southern rail.
Aslef said this action, that it said will involve up to 1,000 members, was over a pay dispute, while the union remains embroiled in a long-running row with the train firm over the introduction of so-called driver-only operation on trains.
Strikes have been set for Tuesday 1 August, Wednesday 2 August, and Friday 4 August.
It said today that members on Southern rail and Gatwick Express had voted overwhelmingly for strike action, with a 61.8 per cent vote in favour of walkouts on a turnout of 80.8 per cent.
Mick Whelan, general secretary of Aslef said:
Now is the time for Chris Grayling and the department for transport to step in and assist in finding a resolution to a problem they caused.
Aslef members are also in the midst of an overtime ban regarding their dispute with the firm over driver-only operated trains.
A spokesperson for Southern's parent company Govia Thameslink Railway (GTR) said:
To call three days of strikes spread across a week is a deliberate move to cause maximum disruption for passengers. To do so in protest against an offer to increase pay by 24 per cent is simply breathtaking. Commuters, the vast majority of whom are seeing pay rises many times less, will understandably be as shocked and frustrated as we are.
We absolutely need to modernise in order to increase capacity on this, the most congested part of the UK's network, where passenger numbers have doubled in places in as little as 12 years. That requires modernisation of infrastructure, trains and working practices. The trade unions must join us in that endeavour.
Earlier today, it was announced that GTR would be hit with a £13.4m fine to fund improvements on the network.
Southern has been involved in a long-running row with both Aslef and the Rail, Maritime and Transport (RMT) union over changes to the role of the guard.
In a letter to GTR boss Charles Horton, transport secretary Chris Grayling said that the long-running industrial action "does not fully explain the poor performance that passengers received".
The firm had been arguing that severe delays and cancellations were mostly down to sickness and industrial action outside of its control, and argued last year that this constituted force majeure, so it couldn't be held accountable for breaching contractual commitments.
GTR said it was pleased that the DfT had settled its force majeure claim for the disruption caused by the industrial action on Southern. The firm said it regarded it as a "fair outcome which draws a line under an issue that has been hanging over the franchise for many months."