The Greens, Sinn Féin and a number of independent TDs have joined forces to form a technical group making it the second biggest opposition body in the Dáil.
The parliamentary pact allows the group greater access to Dáil facilities and more time to question the Taoiseach during question time.
The group said that they were left with no choice to form the alliance having exhausted the negotiation process and having raised the issue in the Dáil chamber on many occasions.
The six Green TDs, the five Sinn Féin TDs and 11 Independent Deputies have written to the Ceann Comhairle Dr Rory O'Hanlon formally requesting recognition as a group as provided for under Dáil standing orders.
Under Dáil regulations a group must have at least seven deputies to be entitled to full party privileges.
Each party and each non-party deputy will maintain their independence and identity. The group will announce its formation this afternoon.
A Green Party spokesman described the plan as a "marriage of convenience", but pointed out that it in no way meant a policy alliance of the parties involved.