The Public and Commercial Services Union (PCS) has backed a major anti-Trident demonstration which is due to take place in central London on 27 February.
Ministers' attempts to turn neighbour against neighbour in a bid to drive through the one per cent benefits cap are a "stain on our society", says PCS.
Public sector unions planing a day of action over government cuts are aiming to build alliances with private sector workers and the wider anti-cuts movement.