What is the 16th Amendment Act?

The Sixteenth Amendment Act of 1963 has two provisions as follows:

• Empowered the state to impose further restrictions on the rights to freedom of speech and expression, to assemble peacefully and to form associations in the interests of sovereignty and integrity of India. 
• Included sovereignty and integrity in the forms of oaths or affirmations to be subscribed by contestants to the legislatures, members of the legislatures, ministers, judges and CAG of India. 

Further Reading:

• Important Amendments in Indian Constitution
• Oaths and Resignations