TUV leader Jim Allister has accused the First and deputy First Minister of "ducking and diving" after he proposed inviting the Queen to Stormont to mark the centenary of Northern Ireland.
Mr Allister was commenting after Arlene Foster and Michelle O'Neill said it would be "inappropriate" to respond to his written question on the matter.
The North Antrim MLA proposed inviting the monarch to Parliament Buildings to address the Assembly to mark the establishment of Northern Ireland in 2021 and the first sitting of the Northern Ireland Parliament.
Mrs Foster and Ms O'Neill declined to respond on the basis that questions should not refer to hypothetical matters.
"In the absence of any specific proposal by the Assembly for such an invitation, and taking into account the prohibition in Standing Order 19(2)(e) on hypothetical questions, we do not consider it appropriate to respond in the terms requested," the written response said.
Mr Allister said he was "disappointed, if not terribly surprised," by the answer.
The Queen addressed the Scottish Parliament as part of its 20th anniversary celebrations in 2019 and has addressed the Welsh Assembly on a number of occasions. The Stormont Assembly is the only devolved legislature she has never addressed.
The veteran unionist said 2021 was a date which should be celebrated.
"What better way to do that than have Her Majesty address the Assembly," he said.
"Why is there such a reluctance to dodge an invitation for Her to address the Northern Ireland Assembly?" Mr Allister queried.
“Once again Northern Ireland is being treated as a semi-detached part of the UK with the fact that this question went unanswered for a full month testament again to the unworkablity of the system.
“There is nothing hypothetical about the centenary of Northern Ireland. It is disappointing that the DUP leader is ducking and diving on the issue."
On Wednesday Sinn Fein said the party's vice-president Mrs O'Neill was "not available" to meet the Duchess of Cambridge during her surprise visit to Northern Ireland, despite an invitation.
She was met by DUP leader Mrs Foster on arrival at Belfast City Airport.
The Queen made her first visit to Northern Ireland as monarch just months after her coronation in July 1953.
As part of the celebrations the Queen and Duke of Edinburgh attended a Garden Party at the Stormont Estate.
Around 20,000 people gathered in the grounds of Stormont for a Royal visit in June 2012 to mark the Queen's Diamond Jubilee.
Northern Ireland's centenary is set to be marked with large-scale celebrations next year, with major events and exhibitions planned.
The plans are set to be similar to events marking Northern Ireland's 50th anniversary in 1971.