The Indian president has approved a bill which bans the slaughter of cows and the sale and consumption of beef in the western state of Maharashtra.
Anyone found breaking the law will face a fine and up to five years in prison.
Hindus, who comprise 80% of India's 1.2bn population, revere cows and the sale and consumption of beef is banned or restricted in many states.
Correspondents say most beef sold in India is actually from water buffaloes which are not considered sacred at all.
But in Maharashtra, buffalo meat, generally seen to be of inferior quality, makes up only 25% of the market and the ban is likely to be felt more keenly there.
The state includes India's commercial capital and biggest city Mumbai.mumbai ] [ maharastra ] [ cow protection ] [ cow ] [ slaughter ]