At least nine people were killed as protesters led by India's Dalits set fire to police posts and blocked railway tracks after the Supreme Court barred the immediate arrest of people accused of discriminating against them, local media said.
Four people were killed in the central state of Madhya Pradesh, where police also imposed a curfew, Indian television channels reported. Three others were killed in other states, local media said.
Reuters could not independently confirm the death toll.
Prime Minister Narendra Modi's government submitted a review petition to the Supreme Court on Monday, asking it to amend the March 20 judgment that sparked the protests, Home Minister Rajnath Singh said in a televised interview.
Dalits are at the bottom of India's ancient caste hierarchy and together with the scheduled tribes - indigenous peoples who are often isolated or disadvantaged - form about a quarter of the population. Protesters carried banners demanding a nationwide shutdown, saying the judgment was diluting the law.
Television showed police beating protesters and an unidentified person firing shots, with demonstrators in the northern state of Haryana also setting police posts ablaze and attacking shops.
Violence was reported from other states such as Rajasthan, Uttar Pradesh, Jharkhand and Bihar, while exams have been postponed and internet services have been shut down due to clashes in Punjab.