The Enforcement Directorate has called Poonam Jain, the wife of jailed Delhi Health Minister Satyendar Jain, for questioning next week.
Mr Jain, 57, was arrested by the central probe agency on May 30 under the Prevention of Money Laundering Act (PMLA) over alleged hawala transactions with a Kolkata-based firm in 2015-16.
A hawala system involves two parties transacting money with local agents on their behalf without the funds passing through formal banking channels.
The Central Bureau of Investigation (CBI) filed a case against Mr Jain and his family in August 2017 for alleged money laundering of up to Rs 1.62 crore.
The CBI alleged Mr Jain and his family set up four shell firms - companies with no real business - to launder Rs 11.78 crore in 2011-12 and Rs 4.63 crore in 2015-16.
The Enforcement Directorate started its probe based on the CBI's first information report, or FIR. In April, the ED had attached assets worth Rs 4.81 crore of Mr Jain's family and of the companies "beneficially owned and controlled" by him as part of the probe.
He is accused of laundering money through four companies allegedly linked to him. The money was used to buy land, the Enforcement directorate said.
Mr Jain's lawyer has earlier said the companies were not controlled by him as he had a very small share. "Companies and shareholders are separate entities. The property of the company is not considered as the property of shareholders," he said.
Mr Jain's arrest had started a fresh war between Delhi Chief Minister Arvind Kejriwal and the central government, over the alleged misuse of central agencies to harass political opponents.
A special CBI court on June 27 extended the judicial custody of Mr Jain till July 11.