The western Indian state of Gujarat has passed a law making the slaughter of cows punishable with life imprisonment.
Under an amendment to the state's Animal Preservation Act, those found guilty of transporting beef will also be jailed for 10 years.
The cow is considered sacred by India's Hindu majority, and killing cows is illegal in many states.
But the new amendment means Gujarat now has the toughest laws on the issue in the country.
Offenders will face heavy fines, as well as time behind bars. The penalty for either act has been doubled from 50,000 rupees ($771; £618) to 100,000 rupees.
Gujarat Minister of State Pradipsinh Jadeja told reporters that the cow was a symbol of Indian culture and the amendments to the act had been made "in consultation with the people".
Chief Minister Vijay Rupani has also spoken repeatedly of "harsh" punishment for those who kill cows.
The new laws will come into effect from Saturday.