Strikes by Southern Railway train drivers will now hit the company at the end of January as well as next week.
Members of Aslef were due to walk out for six days from Monday in a bitter dispute over driver-only trains.
The union changed the dates to January 10, 11 and 13 but announced three fresh strikes on January 24, 25 and 27.
A 6 day strike by drivers on Southern Railway from Monday has been cut to 3 days, but there is a likelihood of further action - @ASLEFunion— Alan Jones (@AlanJonesPA) January 4, 2017
Southern Railway train drivers will strike on January 24, 25 and 27 as well as for three days next week - @ASLEFunion— Alan Jones (@AlanJonesPA) January 4, 2017
Aslef general secretary Mick Whelan said: “We are taking a longer-term view of this trade dispute. The company has not been prepared to move – it is simply going through the motions, turning up at Acas, as it did yesterday, and telling us that it intends to impose driver-only operation.
“We remain committed to a negotiated settlement, as was reached with ScotRail, but it is difficult to negotiate with people who are not prepared to be flexible.
“We still believe a deal can be done but we are, at the moment, a long way from that position.
“It is time for the company to come up with a genuine offer rather than carry on posturing.”
Mick Whelan (Nick Ansell/PA)
The union had reduced next week’s action out of consideration for how long the dispute will last and because of concerns from the public about the impact of a week-long stoppage.
Southern’s passengers have suffered months of disruption because of industrial action, staff shortages and other problems.
Aslef members are currently banning overtime, which is leading to services being cancelled or delayed every day.
The Rail, Maritime and Transport (RMT) union is also embroiled in a dispute with Southern over changes to the role of conductors, which has led to a series of strikes.
Mr Whelan said Aslef members continued to have safety concerns about driver-only trains, claiming the union had raised issues which had been ignored.
A leaflet will be handed to passengers next week with images of platforms from monitors issued by the company, compared with photographs taken by drivers which are blurred and dark.
Mr Whelan accused the Government of being behind the dispute, saying the Transport Department had a “perverse belief” that driver-only trains would lead to quicker services.
He said there was a 25% shortage of drivers on Southern which is why the overtime ban was having such an impact.
He said he had great sympathy with passengers caught up in the chaos and revealed that some drivers had been verbally abused. But he added that his members were “incredibly angry” at driver-only trains being extended without agreement.
Southern Rail said none of its train services will run during next week’s drivers’ strike.
It announced it is putting in place a number of alternative measures to try to help commuters who have essential travel needs.
The company is organising 200 coaches or buses each day to provide road links for essential travel from nine Southern stations into nearby neighbouring networks where they can connect with other train operators’ services.
The fleet has been pulled from a wide range of bus and coach operators across the South East.