Leaders of the country's biggest trade unions are set to oppose any moves at Labour's annual conference to scrap the Trident nuclear weapons system.
Jeremy Corbyn has called for an end to the UK's "weapons of mass destruction", but acknowledged that "differences of opinion" will emerge when the issue is debated at the Brighton conference later this week.
Len McCluskey, general secretary of Unite, which has thousands of members in the defence industry, said his main focus will be the protection of jobs.
"I understand the moral case and the huge cost of replacing Trident, especially in this era of austerity, but the most important thing for us is jobs and the defence of communities.
"We will vote against any anti-Trident motion. I don't think this will be a problem for Jeremy Corbyn. He is a great democrat and we are already seeing a refreshing change to the Labour conference, with open debates," he told the Press Association.
The GMB and other leading unions are also expected to oppose any move to scrap Trident, making it virtually certain that any motion would be defeated.
The Labour leader acknowledged he may be unable to persuade members of his shadow cabinet to oppose the renewal of the Trident weapons system and there may be a "difference of opinion" when the parliamentary vote takes place.
The future of Trident is just one area where Mr Corbyn has different views to his colleagues in the Commons, but sweeping changes to the way Labour policy is formed could see the grassroots members who overwhelmingly backed his leadership bid given a greater influence.
The difficulties faced by Mr Corbyn in uniting his shadow cabinet behind him have been highlighted by the debate on the nuclear deterrent.
Shadow foreign secretary Hilary Benn and shadow justice secretary Lord Falconer have both spoken out against abandoning the UK's nuclear capability, and Mr Corbyn said: "We are going to come to an accommodation of some sort."
Hinting that the Labour vote might not be whipped when Parliament decides, he told BBC One's Andrew Marr Show: "We are going to have to discuss it and debate it and come to a philosophical solution to it. But I understand colleagues' views.
"I hope to persuade them that a nuclear-free world is a good thing, that fulfilling our obligations under the nuclear non-proliferation treaty and promoting a nuclear weapons convention is a good thing. They are all signed up to multilateral disarmament, by the way.
"There are many people, military thinkers, who are very concerned, indeed opposed to Trident, because they don't see it as part of modern security or defence. They don't see any situation in which Trident would become an option you would think about using.
"This is a weapon of mass destruction."
Mr Corbyn suggested it would not be "a disaster" if there were two different opinions in the party, but added: "I will do my persuasive best to bring them around to my view."
With conference set to vote on Trident during the gathering in Brighton, Mr Corbyn said he expects the motion finally put to delegates would involve a "series of alternatives" rather than a straight choice on scrapping nuclear weapons.
Former leadership contender Chuka Umunna, who ruled out serving in the shadow cabinet because of differences with Mr Corbyn over issues including Trident, said the party would have to fix its position on such key policies.
"It's not plausible for us as an opposition not to have a position on the defence of the realm," he told a fringe meeting.
"I think at the moment, we are fresh out of a leadership election, we are not long from a general election where we went down to one of our worst defeats.
"I'm all for debate but, ultimately, we are going to have to have settled positions on things if people are to know what it is they are voting for.
"We have got elections in the offing in May, very important elections, and we are going to have many more rounds before the general election.
"If people don't know what the position of the Labour Party is then we are not going to look like a party of government."
Mr Umunna said he welcomed the suggestion that there might be free votes on Syria and Trident but added: "I just don't think it is sustainable for us to free vote everything and, frankly, it's not sustainable for different people in our leadership to be saying different things."