The strike at the Defence Equipment and Support depot in Beith, Scotland, occurred on Friday and involved more than 50 key workers, media reported.
"The strike action, if it continues over a long period, could eventually have implications for missiles going to Ukraine or Faslane," an insider told UK media.
Workers of the weapons depot, which supplies Storm Shadow and Brimstone missiles to Ukraine, plan to go on another strike over low wages on Monday.
The UK Defense Ministry has reportedly launched "contingency measures" to prevent Ukraine’s weapons supplies from being affected.
Western countries have been supplying Ukraine with military aid since the start of Russia's special military operation in Ukraine in February 2022. The support evolved from light artillery munitions and training in 2022 to heavier weapons, including tanks, later that year and in 2023.
In recent months, Ukraine has been pushing to be supplied with fighter jets. The Kremlin has repeatedly warned against further arms deliveries to Kiev.