The Income Tax department on Sunday conducted raids at the residence and other premises of Madhya Pradesh Chief Minister Kamal Nath's former Officer on Special Duty (OSD) Praveen Kakkad.
A team of about 200 I-T department and police officers swooped down on these premises around 3 am and some undisclosed cash was recovered, they said.
The searches are linked to the suspected movement of hawala money during the ongoing polls season and tax evasion.
They said locations in Indore, Bhopal and Delhi (Green Park) are being raided and those being searched include Nath's former OSD Pravin Kakkar, former advisor Rajendra Miglani and executives linked to his brother-in-law's firm Moser Bayer and his nephew Ratul Puri's company.
Both Kakkar and Miglani had resigned from their posts just before the Lok Sabha polls were declared.
In Indore, the raids were conducted by a team of officials, who arrived from Delhi, at Kakkad's residence in Vijay Nagar area and other places associated with him, sources in the I-T department said.
Searches were also conducted at Kakkad's house in Bhopal's Nadir Colony and a couple of other places in the state capital.
They said documents seized during the searches were being scrutinised in detail.
The raids are also being conducted against Kolkata- based businessman Paras Mal Lodha, the sources added.
Kakkad, a former Madhya Pradesh police officer, was appointed OSD to Nath after the Congress-led government came to power in the state last year.
He had earlier served as OSD to former Union minister Kantilal Bhuria during the UPA regime.
Bhuria is contesting the upcoming Lok Sabha poll from Ratlam-Jhabua seat in MP.
Kakkad's family is associated with a number of businesses, including hospitality.
Ratul Puri was last week grilled by the Enforcement Directorate in Delhi in connection with the Rs 3,6000 AgustaWestland helicopters purchase probe.
Reacting to the raids, a Congress leader in MP accused the BJP-led central government of targeting opposition leaders for "political vendetta".
MP Congress' media cell vice president Bhupendra Gupta, also a former OSD to Nath, charged, "The BJP government has been targeting opposition leaders across the country due to political enmity. Due to such act of political vendetta, Andhra Pradesh Chief Minister (N Chandrababu Naidu) and DMK leader M K Stalin had to stage protest against the Centre."
However, the BJP hit back, saying thieves were now having a complaint against the 'watchman'.
"Black money worth crores was recovered during the Income Tax department's raid at the house of private secretary of Madhya Pradesh Chief Minister Kamal Nath. This has made one thing clear that those who are thieves have a complaint against the watchman," BJP's national general secretary Kailash Vijayvargiya said.