Ans: The 'anti-defection law' was passed through an Act of Parliament in 1985 by the government of Rajiv Gandhi. Passed as the 52nd Amendment Act, 1985 provide for disqualification of members of parliament and state legislature on the ground of defection from one political party to another. For this purpose it made changes in four articles 101,102,190,192 of the constitution and added a new schedule contains the provisions relating to disqualification of MP and MLA.
It states that members who do the following will lose their membership any House (which could be at the Centre or in a State) if they:
1. Voluntary resign from their political party from which they have been elected Vote against the direction of their political party (in legislature)
2. Does not vote/abstain from voting (in legislature) despite having a direction to vote from their party. But it does not apply if the member has prior permission from his/her party or the party condones the member's action within 15 days of the voting.
3. Members independent of any political party will lose their membership if they join one after their election to legislature.
4. Nominated members will lose their membership if they join a party within 6 months of their nomination to legislature.
The law provides exceptions from being disqualified as a member of legislature on the following grounds:
When political parties merge with each other entirely When a political party splits into other parties, subject to not less than a third of the members splitting (as per the 93rd Amendment to the Constitution, which can be read here)
When two-thirds (or more) of members belonging to a party join another party without both their parties explicitly merging
The Speaker or the Chairman of the concerned Houses (as applicable) makes decisions on defection matters. If the Chairman or the Speaker defects, the decisions shall be made by a member elected by the House.