Ian Walker, managing director of Glasgow-based Walker Precision Engineering, employs around 150 people in the Tollcross area.
Much of its workload comes from the MoD, producing components for the production of submarines, helicopters and tanks.
Alistair Darling, leader of the Better Together campaign, visited the site and spoke to staff, accompanied by shadow Defence Secretary Vernon Coaker and shadow Scottish Secretary Margaret Curran.
Mr Walker said: "A lot of products we make here are confidential, highly classified. Right now for various programmes we have employees who are security-vetted and approved for those products.
"For us to be a separate country, where is the assurance that the MoD will give us these clearances and allow us to continue to serve them in the way we have been?
"Alistair and his colleagues walked around the shopfloor this morning and chose who they wished to speak to.
"People are perfectly free to give whatever view they wish, but there's a genuine feeling in here that there would be a dreadful uncertainty if we became independent and separate from the UK."
Ms Curran said: "If you want to hear the positive case for Better Together, speak to the workforce. They told us the benefits of what they get as people in the east end, working for a company like this with contracts that wouldn't be possible, certainly not as easily, if we weren't together."
Former Labour Chancellor Mr Darling said that for thousands of people in places like Glasgow, Edinburgh, Fife and Inverclyde, the UK's defence industry is a major source of jobs and economic security.
He said: "Under EU procurement rules countries can reserve to themselves work that is sufficiently high-security or of such national strategic importance that they don't have to put out to tender.
"For example the UK can have its tanker fleet built outside the UK but a warship with all the equipment it carries is a completely different thing.
"If you lose that guaranteed flow of orders in relation to the high-tech end of the market then everything else that happens here is attached to that, because it's the skills and the expertise that you have that allow work to be done here, for civilian aircraft for example."