Strikes had already been announced for every Saturday in January, but the RMT has confirmed there will be further action on Saturday, February 2, 9 and 16.
It is over a row about over guards and rail safety and tomorrow will be the 45th day of action affecting the Yorkshire Coast line.
There will be no trains at all between Bridlington and Scarborough tomorrow and only a limited number during the daytime between Bridlington and Hull.
Bridlington to Scarborough
Replacement buses depart at 1.15pm and 6.08pm
Scarborough to Bridlington
Replacement buses depart at 11.46am and 3.15pm
Bridlington to Hull
Trains leave at 10am, 11.04am, 12.13pm, 1.04pm, 3pm, 4.04pm and 5.59pm
Hull to Bridlington
9.01am, 10.01am, 10.56am, 11.56am, 1.56pm, 2.56pm, 3.56pm and 4.56pm
RMT General Secretary Mick Cash said: “RMT continues to make every effort to get serious and meaningful talks going with Northern but the company are not interested and would prefer to fire off a barrage of misinformation about both the dispute and their intentions to deflect attention from the impact of their behaviour on the travelling public.
“German-owned Northern have made it perfectly clear in emails to staff that they want to run trains without a safety critical guard on board in a move that would wreck both safety and access to services and they should listen to their front-line staff and pull back from that plan immediately.
"The bogus “guarantees” that they are trying to spin up to the travelling public are not worth the paper that they are printed on.
“We thank the public for their support and understanding throughout this dispute over rail safety and access and the union remains ready for genuine and serious talks.”
David Brown, managing director at Northern, said: “More than 50% of all rail journeys in the UK are made on driver-controlled trains and recently the Department for Transport and Transport for the North publicly confirmed that a second person – in addition to the driver – would be retained on Northern services.
“This second person will provide customer service, including meeting customer needs on accessibility, safety, security, ticketing and information. Therefore, there is no reason for the RMT to continue its disruptive and economically damaging strikes but despite this, the RMT continues with its strike action.
“We expect all of our service on Saturdays in January to be extremely busy and are calling on our customers to plan their travel carefully for the coming weekend, check the new timetables well in advance, and make sure they do not rely on the last trains home.”