The strike has been called by the National Union of Rail, Maritime and Transport Workers (RMT).
Thousands of commuters as well as Royal Ascot racegoers will be affected.
Here is everything you need to know about the strike.
When is the strike?
RMT has instructed all guards and drivers working for SWR to walk out between 00.01 and 23.59 from 18 to 22 June – five days in total.
South Western Railway runs services from London Waterloo to destinations in Surrey, Hampshire, Dorset and Berkshire.
A reduced service will run on South Western Railway from tomorrow until 23 June. Some routes will not have any trains, nor run a rail replacement service.
What is the strike about?
The row focuses on the role of guards. The union wants the rail operator to guarantee the role of guards onboard its trains.
The strike is the latest in a series for South Western Railway. There were previous strikes last Christmas, as well as in February and March.
RMT general secretary Mick Cash said: “Our members are angry and frustrated that despite suspending action in good faith, and entering into talks in a positive and constructive manner, South Western Railway have dragged their heels and failed to bolt down an agreement that matches up top our expectations on the guard guarantee.
“For more than three months we have sought to negotiate a conclusion to this dispute and it is wholly down to the management side that the core issue of the safety critical competencies and the role of the guard has not been signed off. It is because of that crucial failure by SWR that we have had no option but to lift the suspension and move back into strike action.”
Which SWR services are affected?
A reduced service will run between Basingstoke, Alton and Woking and London Waterloo.
A reduced service will run between Brockenhurst and Lymington Pier.
An hourly service will run between Salisbury and London Waterloo. A reduced service will run between Salisbury and Exeter, but trains will not stop at all stations.
No trains will run between Salisbury and Bristol Temple Meads. Customers should use Great Western Railways instead.
A reduced service will run between Aldershot and Ascot every 70 minutes. There will be no service between Aldershot and Guildford.
A reduced service will run between Portsmouth Harbour and London Waterloo via Guildford, with two trains an hour – one fast and one slow. Trains between London Waterloo and Haslemere will not run.
Trains will run between Southampton Central and Fratton every two hours. Change at Fratton for services to Southampton.
Trains will run hourly between Portsmouth and Southsea and Winchester. Change at Winchester for services to London Waterloo.
Trains will run every 30 minutes between London Waterloo and Epsom, with no service between Leatherhead and Dorking. A bus replacement service will run between Effingham Junction and Epsom.
An hourly service will run between Surbiton and Guildford via Cobham.
Replacement buses will run every half-hour between Hampton Court and Surbiton.
A reduced service will run between Chessington South and London Waterloo until 19.00.
No trains will run between Shepperton and London Waterloo. Replacement buses will serve some stations.
A half-hourly service will run between London Waterloo and Windsor & Eton Riverside.
Two trains an hour will run between London Waterloo and Reading.
No trains will run between London Waterloo and Weybridge via Staines. Change at Virginia Water for a replacement bus service.
A reduced service will run between London Waterloo and Weymouth. There will be hourly fast trains from London Waterloo to Bournemouth, and an hourly train shuttle service between Bournemouth and Weymouth.
No trains will run between London Waterloo and Poole.
No trains will run from Salisbury to Romsey via Southampton Central.
SWR advises passengers to check the website for updated information on the strike.
Which services are unaffected?
A normal service will run on the circular route between London Waterloo and London Waterloo via Strawberry Hill.
The Island Line on the Isle of Wight is unaffected.
How can I get to Royal Ascot?
Ascot is on the line from London Waterloo to Reading, between which there will be two trains an hour. There will be a service between Aldershot and Ascot every 70 minutes between 10.00 and 21.45.
Additional trains will be operating to Ascot to help with demand, says SWR.
“Queueing systems will be in place at some stations during this event, so it may take extra time to board your train. We recommend you check your journey before travelling and leave plenty of time to complete your journey.”
How can I get to Hampton Court?
SWR says there will be a “limited train service” operating to Hampton Court for the Hampton Court Palace Music Festival. Again, queueing systems will be in place, and travellers should leave extra time.
What does South Western Railway say?
An SWR spokesperson said that the new strikes were “disappointing”, and that it was “committed to finding a solution” to the row.
“We will do everything we can to keep customers moving during these strikes but would like to apologise for the disruption this unnecessary action will cause.
“Passengers are strongly advised to plan their travel in advance as services are likely to be busier than usual because of the strike action. Rail replacement services and ticket acceptance on other bus and rail networks have been organised where possible, whilst fans attending events at Twickenham, Hampton Court, Royal Ascot, and elsewhere, are advised to allow extra time for their travel.
“Customers will be able to see amendments to their train services, as currently published on our website, in journey planning systems from tomorrow. Further information on additional main line peak-time services – over and above the amended timetable – will be announced in due course.”