Kemi Badenoch has accused Keir Starmer of a 'vindictive' plan to pursue veterans through the courts ahead of a crunch vote on Monday.
The Tory leader told Labour MPs to join her party in opposing the Government's Northern Ireland Troubles Bill which former soldiers have branded a betrayal.
The Daily Mail has campaigned passionately to protect veterans who served during this period from vexatious prosecutions.
One of Labour's first acts in power was to announce it would repeal and replace the previous Conservative government's legislation for a conditional amnesty. Writing for the Daily Mail, Mrs Badenoch accused the Prime Minister of 'hounding our veterans through the courts like criminals'.
She questioned why it was such a high priority when ministers were yet to set out a plan to properly fund defence over the next few years.
Accusing Starmer of having an 'obsession with lawfare' which had prompted the attempted surrender of the Chagos Islands, she said she hoped to force 'yet another U-turn'.
She called on Labour MPs to 'examine their consciences' and vote with the Tories against the legislation returning to the Commons. Her intervention came as it emerged that the Armed Forces minister would miss today's crucial vote to carry over the legislation to the next parliamentary session.
Al Carns, a former Royal Marine and serving reservist, will be overseas visiting troops on defensive missions against Iran when MPs vote, The Sunday Times reported.
Writing for the Daily Mail, Mrs Badenoch accused the Prime Minister of 'hounding our veterans through the courts like criminals'
Upon taking office, one of the Labour government's initial moves was to declare the repeal of the Conservative-era conditional amnesty law, pledging to replace it with new legislation
It means the Government's most senior veteran will be absent from the debate about the legislation which is bitterly opposed by former soldiers. Mr Carns, who was a colonel and completed a tour of Northern Ireland in the 2000s, is expected to stand for leader if Sir Keir is challenged or steps down.
The veterans' community say Labour's Bill reopens the door to the prosecution of elderly former soldiers for events which happened decades ago.
The Tory legislation it replaced offered conditional immunity for conduct during the Troubles.
Hilary Benn, the Northern Ireland Secretary, has pledged to introduce measures to protect veterans, including allowing them anonymity and giving them protection in old age.
But veterans' supporters say the legislation will allow for vexatious prosecutions and have called for cases to be reopened only if there is new and compelling evidence. Today's vote will enable the Government to bring the legislation back before MPs and is essential for its survival.
A government source said Carns's trip was long planned. They added that veterans minister Louise Sandher-Jones would be sitting alongside Mr Benn on the front bench.