That's according to representatives of volunteer organizations, Ukrinform reports, citing Reuters.
While the protesters say they allow humanitarian and military aid through, many resources required by Ukraine's armed forces are bought by civilian organizations and transported on commercial trucks, which are not allowed to pass the blockade.
Taras Chmut, head of Come Back Alive, Ukraine's largest military aid charity, said dozens of night-vision systems and pickup trucks as well as hundreds of drones procured by his group had been stuck at the border for several weeks.
"This is not good, because they are tied to projects, timings and deadlines. [...] Things are getting through, but it is slower than it was before," he told Reuters.
He said Come Back Alive was trying to work out a deal with Polish authorities to allow unimpeded passage of their aid, as Kyiv had no choice but to import many crucial items from abroad.
"Pickup trucks all come from abroad, night vision kits all come from abroad. [...] FPV drones generally come from abroad, and this (protest) slows down our work," Chmut said.
The border protests are affecting manufacturers of military equipment, said Viktor Dolhopiatov, who runs Engineering Corps, a non-profit enterprise making various types of equipment used by the Ukrainian armed forces.
"If the blockade continues this could become, and already is becoming, a big problem," Dolhopiatov said.
According to him, the border blockade had delayed supplies of parts for machines in his factory, as well as components for power supply units used in drone engines and radio stations.
The truckers, who let through military cargoes, often do not do so with dual-use goods to bolster the war effort, he said.
A potential way to circumvent the blockade is to ship cargoes in regular cars rather than lorries, but this is much more expensive.