Under Article 252, Parliament can legislate on a State List subject if:
- Rajya Sabha passes a resolution by simple majority
- Two or more State Legislatures pass resolutions requesting such law
- President issues a proclamation of emergency
- Supreme Court directs Parliament to legislate
Answer: Two or more State Legislatures pass resolutions requesting such law
Article 252 enables 'cooperative federalism': if two or more State Legislatures pass resolutions requesting Parliament to legislate on a State List subject, Parliament can make a law applicable to those States (and others that adopt it later). Examples: Water (Prevention and Control of Pollution) Act, 1974; Urban Land (Ceiling and Regulation) Act, 1976.