Protesters have chained themselves to the gates of a factory in an effort to block workers getting in.
Police have been called to EDO MBM Technology in Brighton, East Sussex, where demonstrators showed up early on Monday morning.
The factory, owned by a global technology giant, has worked on parts for aircraft including the F-35 Lightning II warplane.
Anti-arms trade protesters arrived at the factory in the dark hours of Monday morning, with a lock-on beginning at 6am, a spokesman for the protest group said.
A banner has been hung up on the factory’s metal fencing, saying: “Stop the arms trade. Solidarity with Kurdistan.”
Sussex Police said “two or three” people have chained themselves to the railings and officers are in place to monitor the situation.
The police spokesman added: “They are not talking to us directly.
“We are trying to establish what they are intending to do while keeping access open to the premises.
“We have a duty to make sure that employees are not inconvenienced.”
No arrests have been made so far, police said.
The EDO MBM factory, located in Moulsecoomb on the outskirts of Brighton, is owned by Harris Corporation.
The multinational company has a 6 billion US dollar (£4.66 billion) annual revenue with more than 17,000 employees, according to its website.
Harris Corporation specialises in technology innovation for government and commercial customers, including for military aircraft and space applications.
In 2017 its Brighton premises was awarded a contract to develop technology for the UK’s F-35 Lightning II warplanes, the company’s website says.