Train and bus workers in Liverpool are preparing to strike on the same day.
Merseyrail staff will hold another 24-hour walkout in their ongoing dispute about the removal of 220 on-board rail guards from the regional network by 2020.
Transport union the RMT have confirmed that the industrial action is scheduled to take place on Friday, December 22 – the same time as a planned Arriva strike.
Drivers are continuing to stage walkouts in their own long-standing dispute over pay with the bus operator that has brought public transport to a standstill.
Unions GMB and Unite were unable to reach a breakthrough in their latest round of discussions with Arriva bosses but talks are set to reconvene on Friday.
The dual strikes threaten to trigger widespread disruption on ‘Mad Friday’, traditionally a day when most office workers celebrate Christmas with colleagues.
RMT general secretary Mick Cash said: “The fact that we have been unable to make any progress whatsoever with the company means we have no option but to put this action on and the blame lies with Merseyrail and their political supporters.
“The City and Regional Labour leaders need to step back immediately from the terms of the resolution to remove all the guards, that they voted for a year ago this week, which lit the fuse in this dispute.
“Those senior Labour politicians have chosen the wrong side. They need to stand with the many – the passengers, the workers and the people of Merseyside, and not the few – Tory ministers and bosses of the private operator Merseyrail.”
A spokesman for Merseyrail said: ‘This strike just before Christmas is timed to take place at the busiest time of the year, with people out Christmas-shopping, attending festive events, and many commuters still going to work before the holiday period starts.
“As on previous strike days, we will endeavour to provide as many trains as possible, and timetable details will be disclosed over the next week or so.
“We are keen to see an end to this dispute. At the request of the metro mayor, Merseyrail has agreed to independent conciliation with the RMT, with no pre-conditions.”