The Orange Order has rejected the Windsor Framework as the basis for returning to powersharing at Stormont.
In a statement, the Grand Orange Lodge of Ireland said the decision was taken unanimously at a meeting on Saturday.
The framework was unveiled in February as a means of adapting the Northern Ireland Protocol to deal with trade disruption between the region and the rest of the UK.
Last week, the deal was formally signed off by the UK government and the EU later.
The DUP, the largest unionist party in Northern Ireland, has expressed concerns about the framework and has shown no sign of returning to powersharing at Stormont.
A number of unionist politicians, including DUP leader Jeffrey Donaldson, are members of the Orange Order.
In its statement, the order said the Windsor Framework had delivered “limited but welcome” practical adjustments to the protocol.
It added: “These changes were brought about as a result of unionism’s determined and united opposition to its implementation.
“However, it does not resolve the fundamental concerns which were articulated in the text of the Anti-Protocol Declaration of September 2021.”
The Orange Order said many aspects of the framework had been “oversold” and a proposed green lane for goods entering and staying in Northern Ireland was “not a frictionless border”.
The statement continued: “The Windsor Framework continues to treat Northern Ireland as a place apart within the United Kingdom and equal citizenship has not been restored.
“Article 6 of the Act of Union remains in suspension and, as such, Northern Ireland continues to be a ‘semi-detached’ part of the economic Union the Act created.”
The order said the UK government needed to introduce new legislation to protect the trading relationship between Northern Ireland the Great Britain.
The statement concluded: “Like the unionist political parties, we want these issues resolved so we can continue to work to make a Northern Ireland a better place for all.
“However, given the seriousness of the concerns outlined above, the Grand Lodge voted unanimously not to support a return to the Stormont Executive until there is substantial and tangible progress which resolves these fundamental issues.”