The department had carried out country-wide searches in this case last month.
If a satisfactory reply is not received in the next 90 days, their properties would be seized, the IT notification reportedly said.
The I-T department on Tuesday attached 12 plots of land belonging to Rashtriya Janata Dal chief Lalu Prasad Yadav's family members, including daughter Misa Bharti, her husband Shailesh, sisters Ragini and Chanda Yadav, his son Bihar Deputy CM Tejashwi Yadav and former Bihar CM Rabri Devi. It also served attachment notice under the stringent act for assets worth over Rs 9 crore against the family of Lalu Prasad.
Hours after the Income Tax department slapped benami transaction charges against Lalu Prasad's family members, Bihar Deputy Chief Minister Tejashwi Yadav dismissed the charges as "political vendetta".
Violation of the Act carries rigorous imprisonment of up to seven years and a hefty fine.
Earlier, owing to her failure to appear before the court, the Bharti was slapped with two separate penalties of Rs 10,000 with regard to non-compliance with the I-T department regulations, ANI had reported.
The officials added that "a few more such assets will soon be attached in the case". Benami properties are those purchased in others name to hide who really owns it.
The attachment notice has been issued as per provisions of Section 24 (3) of the Benami Transactions (Prohibition) Act.
"Investigation is ongoing and necessary action has been taken today (Monday)", said an I-T official, requesting anonymity.
A chartered accountant named Rajesh Kumar Agrawal was also arrested by the Enforcement Directorate (ED) on May 22 in connection with the case. He has said in statements that he is "not scared at all" and will "continue to fight against fascist forces". Lalu ki awaz dabayenge to desh bhar me karoron Lalu khare ho jayenge. If it tries to silence one Lalu, crore of Lalu will come forward.