Nationalist politicians Ümit Özdağ and Yusuf Halaçoğlu were attacked while they were set to deliver speeches as part of a campaign for a “no” vote in an upcoming referendum, at Bahçeşehir University on Wednesday.

Two are known for their critical stance against the the opposition Nationalist Movement Party (MHP) leader Devlet Bahçeli who support Yes campaign to along with the government. While Özdağ was previously expelled from MHP, Halaçoğlu still keeps its seat at the party.

A group of 30 people broke into the hall just before the two make their speeches and chanted: “It is Bahçeli who is the leader of this movement.” The group also rushed on to the stage and toppled down the stand.

The two remained sitting at their seats and avoided any physical attack.

The incident came only days after Sinan Oğan, another politician who was expelled from MHP was attacked during a similar campaigning speech.

Özdağ and Oğan had opposed Bahçeli and ran against him for leadership of the party before they were expelled.

A referendum on constitutional amendments, scheduled to take place on April 16, will open the way to a switch from a parliamentary system of governance to an executive presidency.