Engineer said both the parties would be summoned and he would consider video evidence, if any, to find the truth.
"The inquiry date has been fixed as Monday in New Delhi. We are not going to sweep things under the carpet. The complaint has to be carefully examined before any decision is made," Engineer said.
Engineer said the inquiry would be conducted as per the ICC code of conduct and a decision will be taken in the interest of the game.
"Everything possible will be done to adjudicate it immediately. The complaint made by the management of the Punjab team has been to referred to me by Lalit Modi, chief commissioner of the IPL for immediate adjudication under the ICC Code of conduct.
"I have already started the process and will be summoning all concerned and will also seek any video evidence recorded by the host broadcaster namely TWI."
Engineer also urged the media to have patience and not stretch much in getting the information on the unsavoury issue.
"Since the process has started I will request the media not to seek any further clarification or information. I will furnish my report to chief commissioner of IPL keeping in view the ICC code of conduct and interest of cricket," he said.
Earlier, Punjab Cricket Association president I S Bindra said they will provide all the logistical support to Engineer to conduct the inquiry.
"Farokh has been asked to adjudicate the matter and a complaint has been forwarded to him. We have been asked (by Lalit Modi) to provide logistic support to Engineer," Bindra said.
Harbhajan allegedly slapped Sreesanth immediately after their Indian Premier League match last night, in which Sreesanth's Kings XI Punjab defeated the Harbhajan-led Mumbai Indians.