MPS in the North-East are calling on the Government to order a rethink of the plan to close one of the region's biggest defence factories.
A final decision to shut the Royal Ordnance Factory at Birtley, near Gateshead, could be made next month - with the loss of 300 jobs.
The future of the factory is being reviewed by its owners, BAe systems.
The four MPs, led by John McWilliam, Labour MP for Blaydon, have tabled a Commons Early Day Motion, expressing "grave concern" at the plan.
BAe is also considering shutting several other Royal Ordnance sites up and down the country.
The MPs say it will result in the transfer out of the UK of "a significant part of our ammunition manufacturing capability".
Their motion deplores this, and calls on the Government to "carry out an immediate review of the effect these closures will have on the UK's ability to conduct all of her defence tasks and commitments".
The Birtley site, which makes shell casings, has seen orders cut back since the end of the Cold War, and a decision by the Ministry of Defence to go for competitive tendering for munitions supplies led to past job losses.
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