Talks aimed at resolving the bitter row over staffing and driver-only trains on Southern Railway are being held over the next two days.
The meeting between the company and the Rail, Maritime and Transport union follows a year of disruption because of a spate of strikes and other issues such as staff shortages.
It will be the first time in months that the two sides have got together to try to break the deadlock and avert more walkouts.
RMT members have taken 31 days of strike action against Southern since the row flared.
The drivers' union Aslef also remains in dispute after two attempts to seek a resolution were rejected by union members.
Talks between Aslef and Southern are expected to be held soon.
Meanwhile the RMT is holding a demonstration outside Parliament on Wednesday to mark the first anniversary of the dispute.