According to Unite, the Government must prioritise procurement that benefits UK jobs and industry out of the £2.9bn extra defence spending allocated in the Budget.
The call came as the Parliamentary Defence Committee held its first evidence session of the new Parliament.
The committee considered the impact of the Budget on defence spending.
Sharon Graham, general secretary at Unite, said: “Government defence spending must be used to secure UK jobs and skills.
“This country has world class aerospace and shipbuilding capabilities.
“Buying British is crucial if we are going to retain them, for the sake of our national security as well as our future economic growth.”
Unite workplace representatives from BAE Systems, Leonardo and Rolls-Royce recently attended Parliament to lobby MPs on spending defence funding.
Steve McGuinness, secretary at BAE Systems Warton and executive council member at Unite, said: “Under the previous Government, too many UK workers lost out on defence procurement work due to it being awarded to foreign competitors.
“As part of its economic growth strategy, it is imperative that the Labour government now seizes the opportunity to support skilled well-paid defence jobs at home.
“A domestic defence procurement policy needs to be part of a new defence industrial strategy.
“This is especially important for the UK’s aerospace sector, which needs support if the country is to retain the ability to independently design, manufacture and assemble fast jets and helicopters.”