Slovak trucking union UNAS chief Stanislav Skala said his team were ready to block the Vysne Nemecke/Uzhhorod crossing, the sole border point for trucks, from 3 p.m. (1400 GMT).

The Slovak hauliers are joining Polish truckers who have been blocking several crossings to Ukraine since Nov. 6. That blockade has redirected some traffic through Slovakia, causing hundreds of trucks to pile up for kilometres on the approach to the border.

Polish and Slovak truckers complain that Ukrainian truckers offer cheaper prices for their services and also transport goods within the EU, rather than just between the bloc and Ukraine.

Truckers in both countries demand that the EU reinstate a system of granting a limited number of permits to Ukrainian companies to operate in the bloc and for European truckers to enter Ukraine. The permits were abolished after Russia's invasion.

"We will block the border and let four trucks through every hour," Skala told Reuters by telephone while driving toward Vysne Nemecke on Friday.

Military supplies, humanitarian shipments, and perishable goods and animal deliveries will also be able to pass, he said.

He said the blockade would be done in both directions by a few passenger cars, and in coordination with police. Truckers will have a team of several people guarding the blockade in shifts, he said.

The next decision would come after Monday's EU transport ministers meeting in Brussels, where Polish, Slovak and Hungarian delegations were expected to raise the topic.

"The only demand is reinstating the permits," Skala said.

"We are not interested in politics, we just have to protect our market."

Operators also wanted enforcement of rules allowing Ukrainian companies to ship to and from the EU but not local carriage within the EU.

The Slovak Transport Ministry said after meeting the hauliers on Wednesday it would relay their demands in Brussels.

Kyiv has said it will not compromise on the question of permits for Ukrainian drivers.

European transport commissioner Adina Valean said on Nov. 29 that Ukraine and the EU cannot be "taken hostage" by the Polish truckers blockading the border. The situation is "unacceptable" and Brussels reserves the right to intervene in ensuring rules are respected and the law applied, she said.

(Reporting by Jan Lopatka in Prague, Editing by William Maclean)

By Jan Lopatka