The Conservative manifesto gives commitment to build four new nuclear missile-armed submarines, Defence Secretary Michael Fallon has said.
He accused Labour of using the nuclear deterrent as a “bargaining chip” with the SNP, which would vote to scrap it reports BBC.
But Labour’s Douglas Alexander said the claims were “embarrassing”.
He told Radio 4’s Today his party would do no deal with the SNP “or another other party” on Trident.
The Conservatives and Labour are both committed to replacing the UK’s ageing fleet of Vanguard class submarines which carry Trident nuclear missiles and maintaining the continuous , at sea deterrent – meaning there is always one nuclear-armed vessel on patrol.
Labour has floated the possibility of reducing the number of submarines from four to three if a continuous deterrent could be maintained, though Labour’s Chris Leslie told the BBC the party’s “current view” was that four were needed.
The Liberal Democrats favour cutting to three, saying the existing system was designed for the Cold War era.
The Clyde-based submarines that currently carry Trident are due to reach the end of their operational lives within the next decade, and a final decision on replacing the system is due in 2016.
The government in 2013 put the bill at between £15bn and £20bn. However, Greenpeace argued it will run to at least £34bn once extra costs such as VAT are taken into account.
The Lib Dems have said ordering fewer submarines would save up to £4bn in the long-term, though that claim is disputed.