Rule 1.
Notice to the Attorney-General or the Advocate-General
In any suit in which it appears to the Court that any substantial question of law as to the interpretation of the Constitution is involved, the Court shall not proceed to determine that question until notice has been given to the Attorney-General for India, if the question concerns the Central Government, or to the Advocate-General of the State, if the question concerns a State Government.
Rule 2.
Court may add Government as party
The Court may at any stage of the proceedings order that the Central Government or a State Government shall be added as a defendant in any suit involving constitutional interpretation if satisfied that such addition is necessary.
Legal Commentary & Landmark Judgments: Order 27A
Order XXVII-A mandates the issuance of statutory notice to the Attorney-General of India or Advocate-General of the State in any civil suit involving a substantial question of law as to the interpretation of the Constitution.
If your civil suit challenges the constitutional validity of a state enactment or municipal regulation, make an express prayer in the plaint for issuance of notice to the Advocate-General under Order 27A Rule 1.