A case has been filed against the contractor but he is yet to be arrested, police said.
Four persons were Tuesday arrested in connection with an attack on Shiv Sena MLA Tukaram Kate in Mankhurd in Mumbai last week, police said.
Anushakti Nagar MLA Kate was attacked by a group of people, armed with a sword, chopper and hockey stick, late night on October 12.
While Mr Kate escaped unhurt, one of his supporters suffered injuries while fending off the attack.
The attackers had fled after one of Mr Kate's bodyguard pointed his service revolver at them, police said.
Trombay police identified those arrested for the incident as Sachin Khandagale, Mangesh Sawant, Vishal Khandare and Suraj alias Sataku Karke.
A police official said that Mahesh Londhe, a contractor carrying out work related to the construction of a metro rail corridor in the area, had allegedly planned the attack.
The official said that Kate, along with local Sena MP Rahul Shewale, had been protesting for locals to be given jobs and some Sena supporters had stopped five dumper trucks, deployed by the contractor, from transporting debris from the metro rail site.
Police believe the attack was carried out as the protest and stoppage of dumper trucks was affecting the contractor's work.
A case has been filed against Londhe but he is yet to be arrested, the official said.
He said that two vehicles, a motorcycle and a sword had been recovered from the accused.
They will be produced in a court Wednesday, he said.