The move marks the AEO's first step towards creating a single trade association (Event, October).
AEO director-general Trevor Foley said: "This is a logical step. It's about pooling resources to tackle issues such as research and promotion. Some BECA members aren't happy that the organisation doesn't get more involved in key areas."
Contractors which have said they intend to join the Association of Exhibition Contractors (AEC) include Stanco Exhibitions, Melville Exhibition Services and Opex Exhibition Services.
Stanco director and new BECA council member John Standerline said: "Stanco wants to be active in the industry and I don't believe that standing outside what the AEO does is sensible. BECA needs to be brought up to date and the AEO has seized the opportunity."
BECA has yet to say if it will take any action against companies that join the AEC. President John Booth accused the AEO of failing to properly consult other associations and of taking decisions "behind closed doors".
"'There was no discussion brought to us beforehand and we are just expected to toe the AEO line," he said.
Opex chief executive Keith Greetham said: "The industry needs one voice and this is moving towards that. It leaves BECA with a stark choice - stay as a fringe association without the support of a major element of the contracting industry, or bring BECA into the AEC."
The AEO says the AEC will strive for closer cooperation between contractors and organisers.
BECA director Lynn Felton argued: "BECA is already part of joint working groups with the AEO and the Exhibition Venues Association - does this mean we don't have equal representation on these? If so, we need to work towards closer representation, not fragment the industry."
The AEC will officially launch on 1 July.