According to Hindustan Times, the case has been filed as an original suit under Article 131 of the Constitution that allows the Supreme Court to hear disputes between government of India and the states.
The Pinarayi Vijayan government's petition says:
While the Hindus from Pakistan, Afghanistan and Bangladesh are covered by the Impugned Amendment Act, the defendant did not consider the issues of the Hindus, primarily of Tamil descend, in Sri Lanka and Hindu Madhesis in Terai of Nepal, whose ancestors migrated to Sri Lanka and Nepal respectively in the eighteenth Century from the then British India.
The petition says that the CAA has ignored other minorities such as the Ahmaddiyas, Shias and Hazaras.
Chief Minister Pinarayi Vijayan, who has been at the forefront of opposing the law, had also previously written to 11 chief ministers to join him in opposing the CAA.