Several dozen owners of transport companies on Monday blocked three major Polish border crossings with Ukraine in protest at what they say is unfair competition from the neighbouring country's businesses.

Trucks lined up at the border checkpoint in Dorohusk, with almost all cargo traffic blocked by protesters who blamed the liberalisation of European Union rules for the slump in their revenues.

"We want the rules of fair competition to be restored," Rafal Mekler, a co-organiser of the protest, told AFP in Dorohusk.

Following Russia's full-scale invasion of Ukraine, the EU waived a system of permits for Ukrainian transport companies to enter the bloc.

According to Polish companies, the move triggered an influx of Ukrainian competitors into the sector, plunging their profits.

"Their costs of servicing a truck, hiring a driver or merely of opening a business or paying social insurance are much lower," Marek Oklinski, a transport company owner, told AFP in Dorohusk.

"They drive the prices down and take the cargo that we used to carry," Oklinski added.

The protesters staged similar blockages at crossings in Hrebenne and Korczowa, pledging to let passenger traffic as well as transport with humanitarian or military aid pass through.

Poland's infrastructure ministry said Warsaw could not meet the demands of the protesting companies by reinstating the system of permits to the Ukrainian carriers, citing EU rules.

"The agreement was reached by the EU... therefore, in practical terms, Poland cannot reintroduce the permits system with Ukraine until the aforementioned deal expires," the ministry said in a statement sent to AFP, calling on the protesters to end the blockages.