The Presbyterian Church's policy on excluding people in same-sex relationships from full membership is at odds with individual congregations' obligations as charities and may not be legal, a member has claimed.
Arthur Acheson, the clerk of session and trustee at May Street Presbyterian Church in Belfast city centre, said the decision by the General Assembly had placed him in an impossible position.
The May Street congregation is a registered charity - and as a charity it has certain obligations.
Mr Acheson argued that the Presbyterian Church's policy - which also denies baptism to the children of same-sex couples - is not compatible with the obligations.
He has called for the Charity Commission, the independent regulator of charities, to investigate the policy and "request an immediate reversal of the decision".
Mr Acheson said: "The Charity Commission for Northern Ireland is wholly committed to equality and diversity in all that it does.
"As a charity trustee of the Church I am similarly committed.
"If I were to implement this decision, as the Presbyterian Church in Ireland obliges me to do under the constitution of the congregation, it breaches the Charity Commission's statutory guidance and threatens my capacity as a charity trustee to demonstrate that the congregation is fulfilling its obligation to be entirely for the public benefit.
"This decision excludes people from being voting members of congregations, presbyteries and the General Assembly.
"It places an unreasonable restriction on the membership of the congregation for this generation who are being denied voting membership of the charity and for future generations who are being denied baptism and therefore communicant and voting membership.
"The decision removes my capacity for good governance of the charity in line with the statutory guidance prepared by the commission."
Mr Acheson said the new Presbyterian policy "will undermine public confidence in the charity and in the range of Charities that constitute the Presbyterian Church in Ireland".
He added: "I need to know if the Presbyterian Church is acting legally, and personally I can't agree with the policy.
"There are plenty of teachings in the Bible which tell us to 'love thy neighbour'.
"The Church's policy and the Charity Commission guidelines do not sit together at all."
A statement from the Presbyterian Church said it was "deeply regrettable" that Mr Acheson had decided on his course of action.
The Charity Commission was unable to respond last night.