Article 13 declares that all laws that are inconsistent with or in derogation of any of the fundamental rights shall be void. In other words, it expressively provides for the doctrine of judicial review. This power has been conferred on the Supreme Court (Article 32) and the high courts (Article 226) that can declare a law unconstitutional and invalid on the ground of contravention of any of the Fundamental Rights.
The term ‘law’ in Article 13 has been given a wide connotation so as to include the following:
(a) Permanent laws enacted by the Parliament or the state legislatures;
(b) Temporary laws like ordinances issued by the president or the state governors;
(c) Statutory instruments in the nature of delegated legislation (executive legislation) like order, bye-law, rule, regulation or notification; and
(d) Non-legislative sources of law, that is, custom or usage having the force of law.
Thus, not only a legislation but any of the above can be challenged in the courts as violating a Fundamental Right and hence, can be declared as void.
Further, Article 13 declares that a constitutional amendment is not a law and hence cannot be challenged. However, the Supreme Court held in the Kesavananda Bharati case (1973) that a Constitutional amendment can be challenged on the ground that it violates a fundamental right that forms a part of the ‘basic structure’ of the Constitution and hence, can be declared as void.