Union minister Ramdas Athawale has been slapped by a man at a public event in Maharashtra's Ambernath town, police said.
The incident took place Saturday night as the Minister of State for Social Justice and Empowerment was coming down from the stage, a police official said.
The accused has been identified as Pravin Gosavi. He was later beaten up by Athwale's supporters.
Gosavi has been shifted to the state-run J J hospital in Mumbai after receiving initial treatment in Ambernath, police said.
The motive behind the attack was not known and police are investigating the matter.