Politicians were threatened on Monday night during a council meeting in Northern Ireland when a small group of loyalists stormed the building.
There were no injuries but the session was disrupted in Carrickfergus, north of Belfast on the Co Antrim coast, police said.
Cross-community Alliance Party councillor Noel Williams said about five protesters infiltrated the meeting.
"They managed to enter the council chamber unhindered without facing any opposition and once inside subjected councillors to verbal abuse, banging on desks and chairs with implements, leaving many feeling threatened," he said.
"It is unacceptable that the town hall was not under police surveillance, especially as violence has broken out at previous protests.
"People have a right to protest peacefully but this incident tonight put many people's safety at risk and must not be tolerated. We live in a democratic society and councillors were meeting tonight as part of this process.
"The Alliance Party has consistently called for protests like these to stop, letting politicians unite as they find a way forward. In the run up to Christmas it is local businesses and the community at large that are suffering."
The disruption came as at least one police officer was injured in new rioting in Belfast as officers were pelted with bricks.
Earlier this month an Alliance party office in Carrickfergus was burned and there have been a series of death threats made against elected representatives in a row over a reduction in the number of days the Union flag is flown from Belfast city hall.
Dozens of Police Service of Northern Ireland members have been injured by violence which erupted earlier this month.
Appeals for the protests to stop have fallen on deaf ears and Belfast traders have warned of a dismal Christmas with the streets relatively empty of shoppers.
Traffic was brought to a standstill as parts of the city became a battleground on Monday evening with police attacked by missile-throwing loyalists in south and east Belfast.
At one stage the PSNI was confronted by a crowd of 200, since dispersed.
Countless roads have been blocked across the city, causing disruption to shoppers and commuters days before Christmas.
Some retailers said their businesses had been devastated by a campaign which has continued since the start of the month.
The Police Service of Northern Ireland said there had been demonstrations in Greater Belfast tonight, including the neighbouring towns of Lisburn and Carrickfergus.
First Minister Peter Robinson and Deputy First Minister Martin McGuinness have appealed for the protests to stop.
Northern Ireland secretary Theresa Villiers met leaders of Northern Ireland political parties to discuss the flags controversy.
"I have today urged Northern Ireland's political leaders to come together to find a way forward to resolve the ongoing protests on flags," she said on Monday.
"It is vital that all the parties work together to make progress towards a cohesive and shared society where decisions on issues like flags can be made in a way which respects different views and takes into account the different traditions and identities of modern Northern Ireland."
She said she understood the strength of feeling but the disruption caused by these protests was damaging Northern Ireland's economy, particularly for retailers heavily dependent on shoppers in the run-up to Christmas.
"The fact that threats and protests continue to impede elected representatives in carrying out their duties also continues to be a major concern."
She said there was a lot to look forward to in Northern Ireland.
"None of us want to see the clock wound back to an era of sectarian tension when there is such important work to be done to rebalance Northern Ireland's economy and boost jobs and growth."