Romania's foreign ministry said the move was "unacceptable".
ADVERTISEMENTHungarian Prime Minister Viktor Orbán has been criticised for wearing a scarf that features a historical map of "Greater Hungary".
Orbán was pictured wearing the garment at a football match between Hungary and Greece in Budapest on Sunday.
The scarf features the borders of Hungary's former kingdom, which includes modern-day Austria, Croatia, Romania, Serbia, Slovakia, and Ukraine.
Orbán's decision to display the map at a public event has been criticised by two of Hungary's European neighbours.
The Romanian foreign ministry expressed its "firm disapproval" and accused the Hungarian Prime Minister of "revisionism".
"Any manifestation of a revisionist nature, regardless of the form it takes, is unacceptable and contrary to current realities and the commitments jointly undertaken by Romania and Hungary," a statement read.
"This attitude is in clear contrast with the atmosphere of openness and revival of bilateral dialogue shown during recent consultations."
The Ukrainian Foreign Ministry said on Tuesday that it will summon the Hungarian ambassador to Ukraine over the matter.
"The promotion of revisionist ideas in Hungary does not contribute to the development of Ukrainian-Hungarian relations and does not correspond to the principles of European politics," ministry spokesperson Oleg Nikolenko wrote on Facebook.
"The Hungarian ambassador will be invited to the Ukrainian foreign ministry and made aware of the unacceptability of Viktor Orbán's actions."
Nikolenko also said Kyiv expected an "official apology" from Budapest for violating its "territorial integrity".
Orbán has previously invoked ire from Hungary's neighbours by sharing images of "Greater Hungary" on social media.
"Football is not politics, let's not see what is not there," he wrote on Facebook on Tuesday. "The Hungarian national team is the team of all Hungarians, wherever they live."
Maps of the historical region include the territories that Hungary lost in 1920 under the Treaty of Trianon, after World War I.
The loss of two-thirds of its land is considered to be a national tragedy by a large part of Hungarian society. Maps of "Greater Hungary" have also been displayed at far-right rallies.
Romanian MEP Alin Mituța described Orbán's behaviour as "irresponsible" amid Russia's invasion of Ukraine and the "annexation" of territory.
"It's a revisionist gesture that puts Orban alongside Putin, who also dreams of border changes," Mituța wrote on Twitter. "He should be sanctioned and isolated by EU leaders in the European Council."
Orbán has previously been accused of provoking tensions over the large ethnic Hungarian community, who live in the Romania region of Transylvania.
ADVERTISEMENT"Europe is facing its biggest security and economic challenges since the end of the Second World War," Czech foreign minister Jan Lipavský wrote on Twitter.
"Unity and cooperation between EU countries is now crucial. Provocation by Hungarian Prime Minister Viktor Orbán is unacceptable."