"We have explored a generous 3.6 per cent pay increase, however the unions' leaderships are insisting on 4 per cent, double the 2 per cent average increase seen across the UK this year.
"We know how important it is for friends and families to get together over the festive season, so whilst we're sorry for the disruption we will keep the majority of our trains running with fully-trained staff on board and at stations.
"We remain open to talks with the RMT and TSSA, and urge them to call off these strikes which will cost their members pay for no gain."
Passengers were warned to check before setting off and told that services would be busier than usual.