The success of the proposed mutual recognition agreement with the United States is in doubt following talks between the Architects' Council of Europe and its counterpart in North America.
The Architectural Registration Boards in both California and New Jersey are refusing to sign-up to the proposals.
And the UK's ARB has admitted that the negative feedback from the two states will leave a question mark over the agreement - which would allow British-trained architects to practise on the other side of the pond.
'It will be up to the architectural community to decide whether it is worth progressing without the support of these two, ' registrar Robin Vaughan said. 'But in the end, California is one of the biggest economies in the world.'
However, Michiel Bourdrez, the chief negotiator for the National Council of Architects Registration Board (NCARB), the umbrella organisation that represents the architects' boards of North America, dismissed these concerns.
'We have a lot of states to get agreement from, ' Bourdrez told the AJ. 'It will always take several years to get them all to sign-up, but I don't think it will damage the proposed agreement too much.'