Karnataka minister D K Shivakumar was taken into custody by Mumbai police outside the luxury hotel where rebel MLAs from his state are lodged.
Fomer Union minister Milind Deora and former Maharashtra minister Naseem Khan, who had arrived to meet Shivakumar, were also detained, an official said.
Shivakumar was almost pulled out by police while he was being interviewed by a TV channel.
The three leaders were taken to the BKC police guest house, the official said.
Earlier Wednesday, Shivakumar was prevented from entering the hotel, prompting him to announce that he won't leave the spot till he gets to meetthe legislators, in a bid to save the Congress-JD (S) government in the southern state.
After reaching the hotel at 8.20 am, Shivakumar, who landed here early in the morning, was stopped by police from entering the hotel. His plea that he had a valid reservation in the hotel fell flat on the police officials' ears.
They told him the legislators staying the hotel had written to Mumbai police chief saying they feared threat to their life due to his arrival there.