Challenged on two grounds:

Against Doctrine of Separation of Powers (executive exercising legislative functions).
Legislature being a delegate cannot further delegate (delegatus non potest delegare).

Courts rejected these grounds due to advantages of delegation.

R. vs. Burah (Privy Council): Held an 1869 Act empowering Governor to extend law as constitutional conditional legislation, not delegated legislation.

Jatindra Nath vs. Province of Bihar (Federal Court): Followed Burah, held only conditional legislation valid. Provision allowing government to modify an Act was held unconstitutional.

Re Delhi Laws Act (Supreme Court):

Seven judges concluded:
1. Doctrine of Separation of Powers is not part of Indian Constitution.
2. Parliament is not a delegate, so delegatus non potest delegare does not apply.
3. Parliament can delegate powers but cannot abdicate its essential legislative function.
4. Power of delegation is ancillary to legislation.
5. Essential legislative functions cannot be delegated.
Essential Legislative Functions: Laying down policy of law and enacting it into binding rule of conduct.
Delegation is valid if: Essential legislative functions are not delegated; proper guidelines are laid down; limits for exercising powers are prescribed.

Types of Delegated Legislation

Skeleton Legislation: Legislature provides broad law, executive fills details.
Power of Inclusion and Exclusion: Executive adds/removes names from lists to which law applies. Generally considered conditional legislation, held valid if sufficient guidelines exist.
Power of Modification of Statute:
- Harishankar Bagla type: Rules valid even if conflicting with other statutes.
- Power of Inclusion and Exclusion: Modifies operation, not provision.
- Delhi Laws Act type: Executive extends enactments with restrictions/modifications. Courts interpret broadly but modifications must be within policy.
- Power of Incorporation by Reference: Executive applies provisions from one statute to another with modifications.
- Power to Include Removal of Difficulty Clause: Gives executive discretion to modify statutes to remove difficulties. Valid if minor modifications, invalid if changes policy.
Power to Impose Tax: Essential legislative function, generally invalid to delegate. Courts apply harmonic interpretation for exceptions:
- Delegation of power to exempt a commodity from tax: Held constitutional; executive better placed to consider impact.
- Delegation of power to bring a commodity within tax purview: Held valid for similar reasons.
- Delegation of power to fix rates of tax: Valid, subject to maximum prescribed by legislature, due to need for flexibility.
- Delegation to a representative body: Upheld (e.g., municipal corporations) due to representative character.
- Delegation to a statutory body: Upheld if properly guided and controlled.

Control of Delegated Legislation - Judicial Control

Done through judicial review applying the doctrine of ultra vires.
Substantive ultra vires: Delegated legislation is beyond the scope of the delegatee's power.
Procedural ultra vires: Delegatee failed to follow mandatory