Some 40 Southwark trade unionists from eight unions met on Thursday of last week to discuss the 30 June strikes.
The meeting—called by Southwark Trades Council, and backed by local union branches and groups—was addressed by executive members from three of the striking unions—the NUT, PCS and UCU.
They agreed that involving wider forces was the key to success and that more strikes were needed to win.
Southwark Save Our Services (SOS) campaign is working with striking unions to arrange a feeder march.
Chris Kelly from the campaign said, “There is the potential for a huge mobilisation—we need to be visiting workplaces, contacting community organisations, and leafleting across the borough.”