Shadow Defence Secretary Jim Murphy has visited BAE Systems in Brough.
899 workers face losing their jobs at the plant in a redundancy consultation which ends on 26 December.
Mr Murphy met union leaders, the site's management and a group of workers among those facing the axe.
Afterwards he made it clear to journalists that BAE should think again about their planned job cuts, saying "These are 899 jobs. But that's also 899 families, 899 livelihoods. This consultation process is ongoing - if at the end of it we're still in the same situation we were when it began, we'll know it was a sham."
He said: "I've come to the plant to meet the workforce and the management to see what more can be done to save these jobs and keep manufacturing in Brough. There's a remarkable history here, and it should have a bright future.
"Today of all days, when youth unemployment has surpassed the million mark for the first time in our country's history, this is exactly the wrong time to be thinking about throwing more people on the dole and scrapheap.
"We have to try and save as many jobs here as we can and the government has to look at what more it can do to help these remarkable men and women, who've done so much to try and keep their job, keep their dignity and look after their families."