In this doc, we can know that why India Called as "Union of India". And in numbers of case laws, why the Union of India represents the Indian Government.

1. India as “Union of India”
[1]
Q.1 Why India called as "Union of
India"?
A. Union meaning: the formation of a
single political unit from two or more
separate and independent units.
The Constitution declares India as a
federal nation in Article 1 of Constitution
of India. Our Constitution is federal in
form, and there is no intelligible
difference among the member states.1
Federalism defined as covenant signed by
political units that surrender their
individual sovereignty to a central
authority but retain limited residuary
powers of government.2
India is a group of member states, which
had acquired by India by treaty, cession,
conquest, etc.; transferred the individual
sovereignty to the Centre for
establishment of Powerful sovereign
central system. No member who is now an
integral part of a union can secede from
the unity.3
States enjoys the status in federal system
of India, by sharing distribution of powers
with her.4
According to the Australian jurist K.C.
Wheare, “The Constitution of India is
federal in nature but unitary in spirit”.
1
Gangaram Moolchandani vs State of Rajasthan
2001 (6) SCC 89. Bench strength: 2.
2
Merriam Webster’s 11th
Collegiate Dictionary.
3
VII Constituent Assembly Debates 43.
4
Basu D.D., Introduction to Constitution of India
21st
Ed. 2013, Lexis Nexis.
Hence, the units are inseparable to the
will of Centre and governs as per the
Indian (central) Constitution. So, India
a.k.a Bharat (the choice of the
Constitutional assembly to register the
nation under a dual and bilingual
identity) is a Union of States.
AND THUS IT IS ALSO POPULARILY
KNOWN AS UNION OF INDIA.
Q.2 Why Union of India is always
been a representative party of
Indian government in Court
Cases?
India have the right to sue and liability to
be sued, as same as other federal
government has so. The Indian
Constitution gives its citizens equal right
to sue the Government of India, before
the court of law.
From the lines of Article 14 of
Constitution, “The State shall not deny to
any person equality before the law or the
equal protection of the laws within the
territory of India”. It is quite clear that the
Courts of Law protect those rights of
Indian citizens which are vested in the
Constitution from any person includes
the Government itself.
In Article 300(1) of Constitution of India5
it is specified that The Government of
5
Article 300(1): The Governor of India may sue or
be sued by the name of the Union and the
Government of a State may sue or be sued by the
name of the State and may, subject to any
provisions which may be made by Act of
Parliament or of the Legislature of such State
enacted by virtue of powers conferred by this

2. India as “Union of India”
[2]
India may sue or be sued by the name of
the “Union of India” and by the name of
States.
The Union and States are juristic persons
capable of owing and acquiring property,
making contracts, carrying on trade or
business, bringing and defending legal
actions just like individuals. Thus the
Government have the absolute right to
sue any private or public being.
But the individual have limited grounds
to sue the Indian government. There are
following grounds available under same
provision:
1. To question any provisions which
may be made by Act of Parliament
or of the Legislature of such State
within the virtue of Constitution,
mentioned in the union list and
laws made by the center under
concurrent list.
(Question of Sovereign immunity
raised in Pand O Navigation
Company V. Secretary of State
for India6)
2. Injury claims against the Union.
(Negligent exercise of powers by
the State officials in N. Nagendra
Rao & Company V. State of A.P7)
3. Conflicts among States or with
States.
Constitution, sue or be sued in relation to their
respective affairs in the like cases as the Dominion
of India and the corresponding Provinces or the
corresponding Indian States might have sued or
been sued if this Constitution had not been
enacted.
Article 300(1) of Constitution of India
have a good reference with section 176(1)
of Government of India Act, 1935, Section
32 of Government of India Act, 1915, and
section 65 of Government of India Act,
1858. In those sections, Government’s
Liability was pronounced.
Unlikely, in international matters the
name of the parties are fixed on the basis
of the "official name" of the country.
Hence, India being referred to as the
"Government of Republic of India".8
6
1861 (5) Bom HCR Appl P.1
7
1994 SCC (6) 205
8
White Industries Australia Limited v. The
Republic of India UNCITRAL (Final Award) 30
November 2011.