The largest civil service union will call for more public sector walkouts at a TUC meeting on Thursday after confirming its opposition to pension changes.
However, the call by the Public and Commercial Services union is unlikely to succeed and could result in a breakaway group of unions taking further industrial action.
Mark Serwotka, the PCS general secretary, said another bout of "co-ordinated strike action" was needed following a meeting of the union's executive, with teachers' unions and Unite among the organisations harbouring similar concerns.
A union source said the TUC meeting of public sector unionswill update senior figures on progress in pension talks but will not be used to set new strike dates.