The protesters say there are too many migrant workers in Maharashtra
A migrant worker has been beaten to death on a train in the western Indian city of Mumbai (Bombay), police say.
The attack is thought to be related to a recent wave of violence against migrant workers from northern India.
Dharamdeo Rai, 25, who was from the northern state of Uttar Pradesh, was travelling with three friends when they were set upon by a larger group.
Police said 17 people had been detained for questioning and that a murder investigation was under way.
Among those being held were activists of the right-wing Maharashtra Navnirman Sena (MNS) party, which has been accused of several attacks on migrant workers in recent months.
MSN claims migrant workers are taking jobs from local people.
The party chief, Raj Thackeray, was released on bail last week charged with inciting violence against migrants. He denies the allegations.
Reports said that the victim had come to Mumbai two months ago and was working in a local steel factory.
A senior police official said Mr Rai was travelling with three friends to his village in northern India.
"At the same time, a group of 10-12 people boarded the same compartment. A clash began over seating, as the four occupied window seats," said Vasant Koregaonkar.
"The four were beaten up after they were identified as north Indians," he told the Indian Express newspaper.
Earlier this week, a migrant job seeker from Bihar was shot dead by police in Mumbai.
Rahul Raj, who was in his early 20s, allegedly shot and injured a passenger on a bus that he had tried to hijack, demanding to meet the politician Raj Thackeray.
Some senior politicians have demanded an investigation, saying police could easily have disarmed the man.
There have been protests in the northern state of Bihar, which borders Uttar Pradesh, over the violence in the Mumbai area against migrants.
Indian Prime Minister Manmohan Singh has reportedly spoken to the chief minister of Maharashtra state, of which Mumbai is the capital, to ensure the security of migrant workers.
Some 37% of Mumbai's 18m population are migrants drawn to the city in search of work.