Samaraweera explained that they joined the opposition as they were unable to accept the government's present policies.
Their move to switch sides caused an uproar in the House prompting the Speaker to suspend sittings for 10 minutes.
The two were sacked after they began criticising President Rajapakse and his brothers who they accused of dominating the government.
Talks between the two sides with the help of intermediaries to resolve differences and get them to rejoin the cabinet failed in recent weeks.
Samaraweera and Sooriyarachchi have alleged that President Rajapakse bribed Tamil Tigers to force minority Tamils in the north-east to boycott the last presidential poll, paving the way for his victory.
They have also alleged there is serious corruption in the government.