Workers on South Western Railway are set to go on strike for eight days over six weeks in the long-running dispute over the role of guards on trains.
The RMT union said rail bosses had "sabotaged" and made a "mockery" of talks over plans to roll out its driver-only operation.
The strikes will take place on 26, 28 and 31 July as well as on 4, 11, 18, 31 August and 1 September.
South Western Rail (SWR) said it was "disappointed" with the RMT's decision.
In a statement, the rail company said it was "surprised" the union had decided to call further strikes, "especially at a time when families want to be out and about enjoying the summer holidays".
"We will continue to seek a resolution and work hard to minimise any disruption to our customers," they added.
A previous planned strike by staff was called off in June by members of the RMT union.
RMT general secretary Mick Cash said: "It was RMT's firm belief that a deal could be done and an agreement reached like we have with other train operating companies but that requires a responsible and grown up attitude from SWR.
"Instead they have treated the whole process with total contempt and that is why we have no option but to confirm a further round of strike action."
Mr Cash accused SWR of putting "private profits before public safety at a time of unprecedented and dangerous pressure on their services".
The RMT has said changing the role of guards and extending driver-only services would compromise staff and passenger safety, which the government denies.