The North's Assembly will hold an emergency session on Tuesday to discuss plans to display Easter lilies, the republican symbol, at Stormont.
Unionists called the emergency session in an attempt to vote down the decision of the cross-party Assembly Commission to display the flowers in arrangements in the Great Hall of Stormont. The commission, which oversees the administration of the buildings, decided on Tuesday to allow the display.
The decision was opposed by the DUP and UUP members of the commission and was only reached when the Alliance member of the commission, Ms Eileen Bell, used the proxy votes of smaller unionist parties to vote in its favour.
The leader of one of the unionist parties said the republican movement's Easter emblem was symbolic of paramilitarism.
Anybody opposed to terrorism for political ends would be concerned at the way this was being used to antagonise the unionist community, said Mr Cedric Wilson, leader of the Northern Ireland Unionist Party.
Mr Jim Wells, the DUP member of the commission, claimed the Assembly was on "a collision course" which could end up in the courts as it was unclear whether the Assembly could overrule the commission.
Sinn Fein said it was planning to enter a "petition of concern" on the vote. This would mean that any vote on the issue would require cross-community support and would be likely to fail.
Dr Dara O'Hagan, who represents Sinn Fein on the Assembly Commission, described the display as a "small step in accepting the principle of parity of esteem", which was "too much for some unionists and shows they cannot live with the idea of equality".