15, Foreign Minister Dmytro Kuleba said on Monday.
After the Russian invasion blocked Ukraine's Black Sea ports, large quantities of the country's grain - which is cheaper than EU crops - stayed in Central Europe due to logistical bottlenecks, hitting prices and sales for local farmers.
The EU in May allowed Poland, Bulgaria, Hungary, Romania and Slovakia to ban domestic sales of Ukrainian wheat, maize, rapeseed and sunflower seeds until Sept. 15, while allowing transit of cargoes for export elsewhere.
The five countries want the ban extended until the end of the year and some have threatened to introduce their own restrictions if Brussels does not act.
Kuleba said Kyiv was "adamantly against" any such steps.
"This move will violate rules of common market," he said during a visit to the Czech capital Prague. "This move will violate the Ukraine-EU association agreement...it will go against the principle of solidarity."
He said Ukraine was ready to seek solutions but that grains should not be hostage to domestic political processes in the countries involved.