In Hamdard Dawakhana and Anr. v. Union of India and Ors., AIR 1960 SC 554, this Court held:
…Thus when the delegate is given the power of making rules and Regulations in order to fill in the details to carry out and subserve the purposes of the legislation the manner in which the requirements of the statute are to be met and the rights therein created to be enjoyed it is an exercise of delegated legislation….
Thus, a delegate of the legislature is conferred with the power to make rules and Regulations to carry out the purposes of the legislation and such rules and Regulations are called delegated legislation or subordinate legislation.
Apex Court has also laid down the grounds on which such delegated legislation or subordinate legislation can be challenged in the Court. In Indian Express Newspapers (Bombay) Private Ltd. and Ors. v. Union of India and Ors. (1985) 1 SCC 641, this Court has observed in Para 75 at page 689:
A piece of subordinate legislation does not carry the same degree of immunity which is enjoyed by a statute passed by a competent Legislature. Subordinate legislation may be questioned on any of the grounds on which plenary legislation is questioned. In addition, it may also be questioned on the ground that it does not conform to the statute under which it is made. It may further be questioned on the ground that it is contrary to some other statute. That is because subordinate legislation must yield to plenary legislation. It may also be questioned on the ground that it is unreasonable, unreasonable not in the sense of not being reasonable, but in the sense that it is manifestly arbitrary…
Again in Clariant International Ltd. and Anr. v. Securities and Exchange Board of India, (2004) 8 SCC 524, this Court held in Para 63 at page 547:
When any criterion is fixed by a statute or by a policy, an attempt should be made by the authority making the delegated legislation to follow the policy formulation broadly and substantially and in conformity therewith.
The grounds on which the validity of a delegated legislation can be challenged have also been discussed at length in Vasu Dev Singh and Ors. v. Union of India and Ors., (2006) 12 SCC 753 in which the Court has reiterated the aforesaid law.