Belfast City Council has started an investigation after footage emerged of a loyalist flute band parading inside City Hall.
Videos shared on social media show uniformed members of the Glasgow band the Govan Protestant Boys performing in corridors and the reception.
The band was attending a centenary dinner in the building for the George Telford Memorial Orange Lodge.
Sinn Féin, SDLP and Alliance Party councillors have expressed concern.
The dinner on Saturday night was listed in council minutes as a celebration of “100 years of the club based at Clifton Street Orange Hall”.
‘Unacceptable in shared space’
Ciarán Beattie of Sinn Féin said he had contacted the council’s chief executive to “demand answers as to how and why this was allowed to happen”.
He said the incident was “disgraceful”, adding: “This sends out the wrong message of the changing Belfast and City Hall which is supposed to be a shared space and open to all.”
He said that the council was investigating whether there had been a “breach of protocol”.
The Alliance Party’s Michael Long said the videos appeared to show “completely unacceptable conduct in the shared space that is City Hall”.
“There’s absolutely no problem with people using [City Hall] to celebrate events,” he told BBC News NI.
“But it shouldn’t be done in a triumphalist way.”
He added the incident was “clearly an attempt to antagonise people”.
SDLP councillor Carl Whyte tweeted that he was “staggered” by the videos.
“City Hall belongs to everyone in Belfast, and to see the main civic building disrespected in such a manner is an outrage,” he added.