RTÉ News understands that the terms of reference for the Commission of Investigation into telephone recordings will be comprehensive.
The Cabinet is due to discuss the issue tomorrow.
It is understood that the views of the Oireachtas Justice Committee, which recently wrote to the Government, will be taken into account.
The committee wants the substantive issue of the tape recordings, the departure of former garda commissioner Martin Callinan and the management of correspondence in the Department of Justice to be included in the terms of reference.
It is understood that the terms will be flexible to take into account other recordings that have emerged or may emerge.
This would indicate that recordings in prisons will be included, but the Cabinet will have to sign off on the terms tomorrow.
It is believed that Mr Justice Nial Fennelly will report back within a year.
The legislation also provides for interim reports.
It is further understood that it will be decided by Mr Justice Fennelly if the commission will carry out its work in public or private.
The Cabinet will discuss the issue in the morning and make a final decision on the matter.