Defence Secretary Ben Wallace and the Tory leadership candidates have been warned against handing a £1.6bn shipbuilding deal to an Indian firm.
Mumbai-based Larsen & Toubro, which describes itself as “India's premier infrastructure developer” has been accused of using “exploitative” labour standards.
According to the GMB union, their workers are paid about a third of the salary of UK shipbuilders, and there were an estimated 95,000 serious injuries at the company last year.
And some 91 workers lost their lives in the last three years, according to the union.
The Fleet Solid Support deal for three 40,000-tonne vessels to resupply Royal Navy aircraft carriers, destroyers and frigates at sea is expected to be awarded later this year.
Four consortia were each given £5million by the MoD to develop their bids.
The shortlist includes Team UK, involving Babcock and BAE Systems, L&T, Team Resolute, led by Spanish shipbuilders Navantia, and Damen Group.
GMB general secretary Gary Smith has now written to Defence Secretary Ben Wallace - and to Liz Truss and Rishi Sunak, warning L&T were not a “suitable supplier of a contract critical to our national security”.
“I urge you to use your powers to put labour standards and the national interest first,” he said.
Mr Smith told the Sunday Mirror: “It’s scarcely credible Ministers are thinking of sending this vital shipbuilding contract overseas when there are real safety concerns."
He added: “The world is becoming less safe and strong defence manufacturing is essential to our security.
“But instead of backing UK yards, Ministers seem to be getting ready to offshore thousands of jobs to a company that benefits from exploitative wages and the sort of state support that is denied to UK yards.
“This Government is in absolute chaos and Ministers have taken their eye off the ball.
“The UK Government must not sell out UK shipbuilding or risk workers’ lives.”
An MOD spokesperson said: “The contract has yet to be awarded and it is some months off in until it is finalised.
"The contract itself ensures that whoever wins will have to integrate the whole ship in the UK and that a considerable amount of the supply chain is also sourced in-country. Our goal is ensure we increase British ship building, unlock investment and skills for the future.”
