Managing director Mari James launched Cardiff-based GJW in early 1999, having previously been vice-chair of the 'Yes for Wales' referendum campaign for the devolved assembly.
James would only say: 'I will be making changes for all sorts of reasons. My personal circumstances have changed.'
According to sources in the Cardiff PA scene, James is considering refinancing the firm's debt and relaunching it under a different name. At least one staff member is leaving the agency.
GJW Wales' clients are believed to include Arriva Trains and the Association of the British Pharmaceutical Industry.
On its website, GJW Wales professes to have become 'the market leader in PA consultancy in Wales'. It cites its advice on the £1.8bn Ministry of Defence Bowman contract, which 'brought the first major MoD investment to Wales', among its achievements.
Morgan Allen Moore, Grayling and Citigate are among the other major public affairs consultancies with offices in Cardiff.
The new £67m Welsh Assembly building, designed by Lord Richard Rogers, opened this Wednesday, 1 March (St David's Day).