Russia’s Foreign Ministry summoned Poland’s Ambassador Katarzyna Pelczynska-Nalecz on April 29 over Warsaw’s refusal to grant entry permits to a Russian motorcycle gang that is closely linked to President Vladimir Putin.

Kremlin officials says Poland has refused to grant entry to members of the motorcycle gang known as the Night Wolves, a group that supported Russia’s illegal annexation of Crimea and whose members have fought on the side of Russia-backed separatists in eastern Ukraine.

The United States has imposed sanctions on the Night Wolves over attacks they’ve made in Crimea and over their recruitment of fighters for separatists in eastern Ukraine.

Poland in 2015 refused the Night Wolves entry when the fiercely nationalistic group was planning to mark the allied victory in World War II against Nazi Germany.

The Night Wolves' leader, Aleksandr Zaldostanov, has frequently appeared in public with Putin.

Based on reporting by Reuters, RIA, TASS, and Interfax