Workers rallied at Tower Hamlets council in east London last week demanding the Labour-run local authority stop its attacks on workers.
Members of the Unison, GMB, NEU and Unite unions gathered outside the town hall.
The four unions are battling against attacks on thousands of workers.
The council wants to sack workers and re-engage them on worse contracts.
Bosses want to slash severance pay, reduce flexitime, attack special leave entitlement, cut travel allowances and shorten paid night work hours.
Paul Mcgarr, an NEU rep in Tower Hamlets, said coordinated strikes “would shut the town hall, council offices and most schools”.
All unions returned high numbers for strikes in indicative ballots. Unison and the NEU have issued notices of formal balloting.
Paul added, “The unions are standing firm. We are also determined to increase the political heat on Labour mayor John Biggs and the rest of the overwhelmingly Labour council.”
Tower Hamlets Unison said the council is threatening workers with legal action using the Tory anti-union laws. It said that “chief executive Will Turley responded to strike ballots by threatening injunctions”.
John McLoughlin, Unison branch secretary, said, “It is truly shocking that any Labour council should employ Tory anti-union laws to try to impose changes to workers contracts.”
He said the borough had “a proud history of support for trade union rights and opposition to Tory attacks”.
Councillors urged to back freedom of speech on Israel
Activists lobbied Tower Hamlets council in east London last week to demand it stand up for Palestinians.
Campaigners presented the council with a petition demanding it amend its acceptance of the International Holocaust Remembrance Alliance definition of antisemitism.
The lobby, organised by the Palestine Solidarity Campaign (PSC), called on the council to alter the definition to allow freedom of speech for Palestine.
Councillors rejected the demand.
But activists will fight on, and plan to launch an east London PSC.