RMT has announced that the nationwide strike action will take place on June 21, 23, and 25.
It is expected to also cause significant disruption on June 22, 24, and 26, when the network will not be operational before 7.30am and a Sunday service will operate throughout the day.
National Rail is strongly urging its customers to only travel by rail if absolutely necessary between June 21 and 26, and where possible, seek alternative forms of transport.
Those that do travel on the railways are asked to expect severe disruption to their journeys as it is anticipated that the journeys which will be able to run are going to be extremely busy.
Great Western Railway is allowing people with tickets for travel on strike days to be able to travel on the day before and up to two days afterwards.
Mick Lynch, general secretary of RMT, said: ‘We have a cost-of-living crisis, and it is unacceptable for railway workers to either lose their jobs or face another year of a pay freeze when inflation is at 11.1 per cent and rising.
‘Rail companies are making at least £500m a year in profits, whilst fat cat rail bosses have been paid millions during the Covid-19 pandemic.
‘This unfairness is fuelling our members' anger and their determination to win a fair settlement.’
The rail industry says that it wants to work with the RMT to bring how it runs its services up to date, so that it is more reliable and more affordable.