South Western Railway strikes planned for Christmas week
Staff at South Western Railway (SWR) are to hold two more strikes in Christmas week on 27 and 31 December.
The 24-hour walkouts are part of the long-running dispute about the future role of guards. A strike has already been announced for 22 December.
The National Union of Rail, Maritime and Transport Workers (RMT) said its action was "a result of the company's intransigence" over the issue.
SWR said the strikes were "totally unnecessary".
In a statement, the firm said it had already offered to meet the union for talks before the latest strikes were announced.
"By announcing further strike dates, the RMT has shown it has no intention of finding a solution and is only interested in inflicting more misery on passengers as they try to enjoy the festive season," it said.
RMT General Secretary Mick Cash said SWR had "stubbornly refused" to ensure that trains would not run without guards.
He said: "South Western Railway are looking for a green light to throw the guard off their trains as and when they see fit in the name of profit."
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The company has previously said guards would be rostered but trains could still operate without them.
A series of strikes about driver-only trains began on Southern railway in April 2016.
RMT members on Arriva Rail North are striking on every Saturday for the rest of the year in the same dispute.
The union previously said it had negotiated "guard guarantees" in Wales and Scotland as well as on a number of English franchises.
SWR has previously run about half of its normal services on strike days.