To understand this question, we need to go back to history.
Post-World War II
World War II started in 1939 and lasted till 1945. It saw genocide, concentration camps and slave labour. Aftermath of this war was very serious. Japan was the biggest sufferer.
During this period there was need felt to have an institution to manage relationship as intergovernmental organization responsible for maintaining international peace and security, developing friendly relations among nations, achieving international cooperation, and being a center for harmonizing the actions of nations. It is the largest, most familiar, most internationally represented and most powerful intergovernmental organization in the world.
The UN was established after World War II with the aim of preventing future wars, succeeding the ineffective League of Nations. The name “United Nations”, coined by President Franklin D. Roosevelt od United States of America. It was first used in the Declaration by United Nations of 1st January 1942, during the Second World War, when representatives of 26 nations pledged their Governments to continue fighting together against the Axis Powers.
Delegates of 50 countries met in San Francisco on 24th October,1945 at the United Nations Conference on International Organization to draw up the United Nations Charter. Those delegates mull over on the basis of proposals worked out by the representatives of China, the Soviet Union, the United Kingdom and the United States at Dumbarton Oaks, United States in August-October 1944.
The Charter was signed on 26 June 1945 by the representatives of each of the 50 countries. Poland signed it later and became one of the original 51 Member States.
The United Nations officially came into existence on 24 October 1945, when the Charter had been ratified by China, France, the Soviet Union, the United Kingdom, the United States and by a majority of other signatories. United Nations Day is celebrated on 24 October each year.
Now you will say why I am discussing UN here. We are discussing UN because in 1951 a Convention was signed under Article 14 of Universal Declaration of Human Rights,1948.
The 1951 Convention, was a post-Second World War instrument, was originally limited in scope to persons fleeing events occurring before 1 January 1951 and within Europe. The Convention came into force on 22 April 1954
Thereafter one amendment was adopted in 1967 Protocol which removed the geographical and temporal limits of 1951 convention. The 1967 Protocol removed these limitations and thus gave the Convention universal coverage. It has since been supplemented by refugee and subsidiary protection regimes in several regions, as well as via the progressive development of international Human Rights Law.
India is not Signatory to the Original 1951 Convention nor of 1967 Protocol and hence India has no Refugee Act.
NOW HOW DOES INDIA CONTROL ILLEGAL MIGRANTS?
For that India has The Foreigners Act,1946. Section 2(a) of the said Act say the Foreigner means a person who is not a Citizen of India. It empowers Government to make orders and law with respect to any particular foreigner or any prescribed class or description of foreigner, for prohibiting, regulating or restricting the entry of foreigners into 1[India] or their departure therefrom or their presence or continued presence therein
Section 3(2) (a) provides the foreigner shall not enter India or shall enter India only at such times and by such route and at such port or place and subject to the observance of such conditions on arrival as may be prescribed;
(b) shall not depart from India, or shall depart only at such times and by such route and from such port or place and subject to the observance of such conditions on departure as may be prescribed;
(c) shall not remain in India or in any prescribed area therein;
(cc) shall, If he has been required by order under this section not to remain in India, meet from any resources at his disposal the cost of his removal from India and of his maintenance therein pending such removal;
(d) shall remove himself to, and remain in, such area in [India] as may be prescribed
Determination of nationality:
When a foreigner is recognised as a national by the law of more than one foreign country or where for any reason it is uncertain what nationality if any is to be, ascribed to a foreigner, that foreigner may be treated as the national of the country with which he appears to the prescribed authority to be most closely connected for the time being in interest or sympathy or if he is of uncertain nationality, of the country with which he was last so connected :
Provided that where a foreigner acquired a nationality by birth, he shall, except where the Central Government so directs either generally or in a particular case, be deemed to retain that nationality unless he proves to the satisfaction of the said authority that he has subsequently acquired by naturalization or otherwise some other nationality and still recognized as entitled to protection by the Government of the country whose nationality he has so acquired.
A decision as to nationality given under this Act shall be final and shall not be called in question in any Court ; unless the Central Government, either of its own motion or on an application by the foreigner concerned, may revise any such decision.
They are Stateless people. They belong to Indo-Aryan ethnic group who predominantly follow Islam with few following Hinduism. They hail from Myanmar and reside in Rakhine State.
During the Pakistan Movement in the 1940s, Rohingya Muslims in western Burma organized a separatist movement to merge the region into East Pakistan. The commitments of the British regarding the status of Muslims after the war are not clear. Muslim leaders believed that the British had promised them a “Muslim National Area” in Maungdaw region. They were also apprehensive of a future Buddhist-dominated government. In 1946, calls were made for annexation of the territory by Pakistan as well as of an independent state. Before the independence of Burma in January 1948, Muslim leaders from Arakan addressed themselves to Muhammad Ali Jinnah, the founder of Pakistan, and asked his assistance in incorporating the Mayu region to Pakistan considering their religious affinity and geographical proximity with East Pakistan. The North Arakan Muslim League was founded in Akyab (modern Sittwe) two months later. The proposal never materialized since it was reportedly turned down by Jinnah, saying that he was not in a position to interfere in Burmese matters.
In 1982, the citizenship law enacted by the Burmese military did not list the Rohingya as one of the 135 “national races” of Burma. It take into account just one survey for defining the history of a group of people is highly problematic. It overlooks the fact that Rohingya were mentioned in records earlier to this survey. This made much of the Rohingya population in Burma stateless in their historical homeland of Arakan.
Citizenship Amendment Act,2019
It gives rights to persecuted minority in our neighbouring Islamic countries
For details see following links