The Rail Maritime and Transport Union has added two new strike days to the action over job security, pay and working conditions on Wednesday July 27.
The new dates are Thursday August 18 and Saturday August 20 and there is likely to be further disruption around these dates mainly caused by trains being in the wrong places.
The stoppages come after Network Rail made an offer of four per cent in the first year followed by a possible four per cent in the second year, conditional on RMT members accepting all attacks on their terms and conditions.
RMT has yet to receive a pay offer or guarantees over job losses from the train operating companies (TOCs).
RMT general secretary Mick Lynch said: “The offer from Network Rail represents a real terms pay cut for our members and the paltry sum is conditional on RMT members agreeing to drastic changes in their working lives.
“We have made progress on compulsory redundancies. But Network Rail are still seeking to make our members poorer when we have won in some cases double what they are offering, with other rail operators.
“The train operating companies remain stubborn and are refusing to make any new offer which deals with job security and pay.
“Strike action is the only course open to us to make both the rail industry and government understand that this dispute will continue for as long as it takes, until we get a negotiated settlement.
“The public who will be inconvenienced by our strike action need to understand that it is the government’s shackling of Network Rail and the TOCs that means the rail network will be shut down for 24 hours.
“We remain open for further talks.”