A group of MPs have said they have found "no legal requirement" that unionists on Lisburn City Council should share power with nationalists.
Michael Mates, chairman of the Northern Ireland Affairs Committee, was responding to a letter from Sinn Féin councillor Paul Butler.
He had questioned whether unionists should be allowed to hold all senior positions on the council, despite a quarter of councillors being nationalists.
Mr Mates said: "I have looked into the questions you raise and am told that there is no legal requirement for district councils to apply the principles of proportionality in the appointment of chairmanships or memberships of committees.
"I am aware of course that many district councils do operate powersharing arrangements on a voluntary basis, and that is something encouraged by the government."
Mr Mates added that "it will not be possible for the committee to inquire" into the questions raised by Mr Butler.
Mr Butler described the response as "disappointing".
"They need to be calling for legislation which makes it binding on district councils to implement proportionality," he said.
"While I welcome Michael Mates' support for powersharing arrangements on a voluntary basis in district councils, he should have also criticised Lisburn council for its exclusion of nationalists."
