Avanti West Coast staff are to take part in a fresh wave of strikes in a dispute over rosters.
Members of the Rail, Maritime and Transport union (RMT) who work as train managers will walk out on October 22 and November 6.
RMT general secretary Mick Lynch said: "Avanti are one of the worst operators we have ever tried to negotiate with.
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"They have treated our members appallingly and this strike action is the culmination of months of neglect and a strong response to the arrogance bosses have shown.
"Avanti should never have been given any extension to their franchise contract for all the chaos they have caused passengers, and their contempt of their staff is part and parcel of their disastrous approach."
An Avanti West Coast spokesperson said: "We're disappointed by the RMT's decision to go on strike in the coming weeks which we think is premature.
"This is completely unfair on our customers who will again bear the brunt of more unnecessary disruption to their plans.
"We would urge the RMT to reconsider this course of action and work with us to resolve this dispute."
It is understood that rosters were introduced earlier this year to help improve the resilience of Avanti's services and further consultation is taking place about December's rosters.
The row is separate from disputes over pay, jobs and conditions across the railway industry which has led to a series of strikes this year.
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