Workers will hold a rally today in protest at a council's decision to derecognise a leading trade union.
Unison appealed to leaders of Plymouth City Council to drop its "macho politics" and hold talks over jobs, pay and conditions.
Unison's offices at the Conservative-controlled council have been closed in the wake of a disagreement over planned changes to wages and conditions.
General secretary Dave Prentis said: "Derecognising the union is an aggressive and disproportionate response to Unison's honest efforts to protect our members' jobs, pay and conditions and protect vital services for local people.
"We will not be pressured into signing an agreement that discriminates against some groups of staff."