Train drivers are staging a series of 24-hour strikes in a row over taxis.
About 200 South West Trains drivers will walk out
Members of the Aslef union based at Waterloo station in south London will walk out next Tuesday and Thursday and again on 13 and 15 June.
They said South West Trains (SWT) had reneged on an agreement to provide taxis to drivers on early morning or late night shifts.
An SWT spokesman said the use of taxis had been "abused", leaving the company to foot soaring bills.
SWT, which runs services from Waterloo to counties across the South East, said only 200 of its 1,200 drivers were involved in the dispute.
"We have decided to get costs under control. We feel we have made a reasonable offer and we are disappointed that strike action has been called," a spokesman said.
"We will continue to do everything we can to stop this unnecessary strike happening."
An Aslef spokesman said the dispute had been going on since 2003 but things had "come to a head".
He added: "Both are in positions which can be best described as entrenched. These strikes will be going ahead."