Rail bosses have asked mediators to help facilitate talks with unions following the announcement of further industrial action.
Govia Thameslink Railway (GTR) has asked arbitration service Acas to intervene in its bitter dispute with the RMT, which plans a five-day strike in August over the role of conductors.
The RMT is also balloting members on further industrial action over cuts to station ticket office opening hours.
GTR chief operating officer Dyan Crowther said: “The RMT’s claims we have refused to engage with them are simply not true and we are calling on them to come to Acas and sort this out for the sake of our passengers.
“Passengers have been suffering daily disruption ever since the RMT began this unnecessary action and should not be forced to suffer five days more, all because the RMT is refusing to work with us and modernise the railway for the benefit of our passengers.
“We have guaranteed all our onboard staff a job, as valued members of our future operation, with no reduction in salary.
RMT general secretary Mick Cash said union officials had repeated their offer to suspend talks, providing GTR suspended planned changes to the role of conductors.
He said: “RMT officials have already cleared the diaries and are available for serious and genuine ACAS talks which is exactly what we have been calling for all along.
“On top of that we repeat our offer in good faith to suspend action if the company agree to suspend the planned changes to the safety critical role of the guard and the bulldozing through of the new contracts without agreement
“That would create the space for talks to take place outside of the pressure cooker. RMT will be at ACAS to discuss the full range of detailed issues at the core of this dispute”.