In this landmark judgment (per Obiter Dicta), Apex Court has held that,

A parliamentary legislation when it receives the assent of the President of India and is published in the Official Gazette, unless specifically excluded, will apply to the entire territory of India. If passing of a legislation gives rise to a cause of action, a writ petition questioning the constitutionality thereof can be filed in any High Court of the country. It is not so done because a cause of action will arise only when the provisions of the Act or some of them which were implemented shall give rise to civil or evil consequences to the petitioner. A writ court, it is well settled, would not determine a constitutional question in a vacuum.

The court must have the requisite territorial jurisdiction. An order passed on writ petition questioning the constitutionality of a Parliamentary Act whether interim or final keeping in view the provisions contained in Clause (2) of Article 226 of the Constitution of India, will have effect throughout the territory of India subject of course to the applicability of the Act.

Citations: [2004 SCALE 5 304], [2004 AIR SC 2321], [2004 SCC 6 254], [2004 BOMCR SC SUPP 2 654], [2004 AIR SC 2766], [2004 SUPREME 3 757], [2004 JT SUPP 1 475], [2004 ALLMR SC 5 700], [2004 DLT 111 480], [2004 COMPCAS 120 672], [2004 ELT 168 3], [2004 AIC SC 19 730], [2004 BC 3 56], [2004 COMPLJ SC 3 1], [2004 CTC 3 365], [2004 DRJ 77 317], [2004 ECR SC 114 1013], [2005 ECR SC 118 151], [2004 ELT SC 186 3], [2004 JCR SC 3 92], [2004 JT SUPPL SC 1 475], [2004 PLR 138 626]

Other Source links: https://indiankanoon.org/doc/1876565/ and https://www.casemine.com/judgement/in/5609ae06e4b0149711412bc2

See this, this, this and this Supreme Court Judgments. Many High Courts have relied on the above aspect of this Judgment here.