The National Union of Rail, Maritime and Transport Workers (RMT) has blasted the reason behind tomorrow's Northern train cancellations as "nonsense".
A total of 49 services will not be running tomorrow, something Northern said is "due to some train crew having made themselves unavailable to work".
It will see 18 cancellations from Blackpool South to Colne and Dalesrail Blackpool to Carlisle, 29 cancellations from Wigan North Western to Liverpool, and two part-cancellations from Lancaster to Morecambe.
And for those jetting off on holiday, a further 30 cancellations will also be in place between Liverpool and Manchester Airport.
A spokesman for the RMT union said: "It's nonsense. They just haven't got anyone to work for the day in question.
"It's not down to the staff it's down to the company. They are heavily reliant on people giving their time off to work for the company.
"It's optional and not down to staff to sort out gaps.
"It makes it sound like it's down to the drivers. You can't just just not turn up for your job or you would get fired."
They added: "They don't employ enough staff to start with. They are trying to make staff give up their days off.
"If you have two days off a week and a company says 'come and work' you can say no, you might have family or other things to do."
These comments were put to Northern, who said: "In some contracts that train crew have there is no requirement to work on Sunday; they are voluntary only.
"They can give seven days notice not to work on the Sunday.
"Sundays are entirely voluntary on these contracts so they can choose not to work them - but they have to give notice.
Regarding RMT's claim about driver shortage, a spokesman added: "We have more than enough drivers to operate our trains in normal conditions.
"We have more now than at the start of the franchise."