Step 1: Understand the Anti-Defection Law.
This law, introduced by the 52nd Amendment and contained in the Tenth Schedule of the Constitution, is designed to prevent political defections by legislators. It provides for the disqualification of Members of Parliament (MPs) and Members of State Legislatures (MLAs) on grounds of defection.
Step 2: Identify the deciding authority as per the Tenth Schedule.
The law explicitly states that any question regarding the disqualification of a member on the ground of defection shall be referred to the presiding officer of the House, and his/her decision shall be final.
For the Lok Sabha, the deciding authority is the Speaker.
For the Rajya Sabha, the deciding authority is the Chairman.
For a State Legislative Assembly, it is the Speaker.
For a State Legislative Council, it is the Chairman.
Step 3: Note the role of the judiciary.
Initially, the decision of the presiding officer was not subject to judicial review. However, in the \textit{Kihoto Hollohan v. Zachillhu} case (1992), the Supreme Court held that the presiding officer's decision is subject to judicial review on grounds of mala fides, perversity, etc. But the primary and original authority to decide the case remains with the Speaker/Chairman.