Hungarian opposition leader Peter Magyar put European Union membership for Ukraine at the centre of his campaign against nationalist Prime Minister Viktor Orban at a major rally Sunday.

The former government official, who has emerged as the main rival to the longstanding prime minister, promised a referendum on the divisive topic as he revealed the results of a nationwide survey carried out by his party.

Magyar, 44, and Orban, 61, have stepped up political hostilities as the country heads for a legislative election in a year’s time. Thousands cheered Magyar in Budapest on Sunday, a day after Orban’s followers held a demonstration outside the European Union offices in the Hungarian capital.

Magyar said more than 1.1 million people, from a population of 9.6 million, had answered questions in his “Voice of the Nation” survey carried out over the past month by thousands of supporters.

According to videos shared on social media, some of the volunteers were attacked by followers of Orban, an outspoken critic of the EU.

The 13 questions ranged from pensions to Hungary’s international challenges.

Magyar’s Tisza party said that 98 percent of those who answered backed Hungary’s membership of the European Union, while 58 percent supported Ukraine’s EU membership bid.

“The results show that the subject divides society and so will be put to a legally binding referendum when we take power,” Magyar told the rally.

Hungary, he added, would again become “a proud and trusted NATO ally and a complete part of the EU”.

Tisza now poses the biggest threat to Orban’s rule since he became prime minister again in 2010. Several polls have indicated that Orban’s Fidesz has lost its lead over the opposition.

Orban has said that Ukraine’s membership of the EU would “ruin” the 27-nation bloc.

The government has said it will sent out ballots next week for a non-binding poll on whether Ukraine should be allowed into the bloc. It has previously used such polls to back its anti-EU stance.

A document accompanying the ballot claimed without offering evidence that EU finance intended for Hungary would be diverted to Ukraine, that “cheap labour” from Ukraine would take jobs from Hungarians and that epidemics would spread because not enough Ukrainians have vaccinations.

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