While negotiations on the Mutual Recognition Agreement (MRA) are advanced, it has emerged that there are high-level concerns from European bureaucrats over the American side of the deal.
If the MRA was to win the go ahead it would dramatically ease the process for EU-trained architects registering to work in the US and vice versa.
It would radically transform cross-Atlantic ties in architecture and almost certainly see more Americans working in Europe and more Europeans working in the States.
The negotiations to date have been between the Architects Council of Europe - of which the ARB and the RIBA are members - and the National Council of Architects Registration Boards (NCARB) on the other side of the Atlantic.
However, it has emerged that those on the European side of the international deal are worried because NCARB is not recognised internationally.
If this is not changed - and there is no immediate likelihood of this happening - the future of the deal with remain uncertain.
'It is extremely hard to tell what is going to happen,' a source on the negotiations told the AJ. 'We are breaking new ground, but we don't know what will happen because there is no internationally recognised interlocutor on the other side.'