The Maharashtra Navnirman Sena, the workers of which clashed with Samajwadi Party activists prior to a UNPA rally in Mumbai on Sunday, said its members were "provoked".
"We were provoked to act the way we have," MNS spokesperson Shishir Shinde told the media in Mumbai.
When a rally is being organised, the party needs to make sure there are no obstructions for the traffic and pedestrians, he said.
"When in Maharashtra, they must act like Maharashtrians. They (referring to SP) must adopt our way like saying Mumbai and not Bambai," added Shinde.
The clash started after MNS workers allegedly attacked a bus carrying SP workers near Kherwadi in suburban Bandra.
The police used batons to bring the situation under control and also detained seven MNS workers.
Additional security personnel have been deployed in Dadar area, where the rally of United National Progressive Alliance (UNPA), of which SP is a key constituent, is being held.
The Raj Thackeray-led MNS has been targeting north Indian migrants living in the metropolis and taken objection to celebrations like Chhat pooja and Uttar Pradesh Diwas in Mumbai.
Congress spokesperson Sanjay Nirupam, himself a north Indian, condemned "the MNS attack on SP workers" and said nobody "instigating violence should be spared".
The government should take appropriate action against them, he said.