The GMB's Paul Kenny, who represents 639,000 workers, called a conference of defence workers warning a vote could cost tens of thousands their jobs.
Paul Kenny spoke out today after Mr Corbyn said a poll of 380,000 party members could ditch Labour's pro-nuclear policy after 25 years - reducing the say of the shadow cabinet, conference and national executive.
But the GMB general secretary, who represents 639,000 workers, warned tens of thousands of them could lose their jobs.
Mr Kenny hit back by announcing he will call a special conference of Britain's defence workers to ask their view.
Corbyn will also face opposition from Unite the Union as Daily Telegraph reported shortly after the Shadow Cabinet reshuffle:
It is highly unlikely that Unite will decide that it should support a policy change that would put its members out of work. It is even less likely that Len McCluskey will risk his own internal authority in the union – from which he derives his power in the Labour Party – on making his own members redundant.
The policy will not go down with Labour voters or the public in general either as the world is an increasingly dangerous place with North Korea exploding an H Bomb (much to the consternation of the Chinese, let alone anyone else) and terrorism remains the main threat to world stability.
In order to defend ourselves there is a need to retain not just armed forces ready to act on behalf wherever they are needed but also and strong and viable indigenous defence industry with a skilled work force to produce British weaponry as required for our defence.
Britain's defence cannot be undermined by the anti-Western clique around Corbyn. Only our enemies will gain from this. the struggle for Labour is more than just for a party it is also for our nation.
Corbyn cannot be trusted nor can his friends.