Chief Opposition Whip, UNP MP John Amaratunga said that the UNP will take part in the process only if some conditions are met.
The Cabinet had last week decided to change the clause where the provinces can be merged under the 13th Amendment to the Constitution.
Cabinet spokesman Minister Keheliya Rambukwella had announced last week that a PSC will be formed this week to propose changes to the other clauses in the 13th Amendment.
Amaratunga added that among the conditions for the UNP to be part of that process is the full implementation of the recommendations of the Lessons Learnt and Reconciliation Commission (LLRC).
The UNP also wants the 17th Amendment to be implemented and the media, police and state institutions to be given the freedom to operate independently.
The government is expected to name the PSC on Tuesday and Amaratunga said that if the UNP is invited to name its members to the committee it will refuse to do so.