Prominent loyalist Jamie Bryson is among those who have held discussions with the DUP-convened panel set up to consider the Windsor Framework.
Friday's meeting with the Peter Robinson-chaired panel at La Mon Hotel near Belfast came as the EU and UK adopted the revised post-Brexit trade arrangements.
The eight-person consultative group is expected to publish its findings next week.
The signing-off of last month’s agreement has prompted further calls for the DUP to end its boycott of the Stormont institutions.
First minister-elect Michelle O’Neill said it was “time to move forward”.
“The negotiation is over and the deal is done,” she said.
SDLP leader Colum Eastwood is expected to tell his party conference in Derry that unless Stormont’s parties can work together “there must be a new model of shared stewardship between the British and Irish governments”.
“One-tradition rule is gone and it is never, ever coming back,” he will tell members.
The meeting between the panel and Mr Bryson comes amid speculation that the party is poised to reject the framework. The prominent loyalist has already rejected the deal, as have high-profile unionist politicians including DUP MP Ian Paisley.
When contacted by The Irish News yesterday, Mr Bryson said: “I do not discuss the content of private meetings.
“I welcome the opportunity to positively engage with the panel led by Mr Robinson and look forward to hearing the outcome of their diligent work and extremely worthwhile engagement.”
Writing for the Unionist Voice website, Mr Bryson previously said: “The Windsor Framework does not restore the Acts of Union. Indeed, it may be said that it entrenches the subjugation.”
It is understood several meetings involving the panel were held this week and members are due to reconvene next week.
Earlier this week Secretary of State Chris Heaton-Harris told DUP leader Sir Jeffrey Donaldson there would be no further talks around the deal, which was agreed after months of negotiations.
“The two sides to those negotiations which have concluded, the UK government and the European Union, are going to make the framework work,” he said.
A spokesman for the DUP declined to comment but indicated that the panel was established by the party leader to work independently.
