Sources said former Deputy Chief Minister Tejashwi Yadav was called at 10.30 am for his questioning. His mother Rabri Devi was examined by tax officials later, starting 2 pm. Lalu Yadav's daughter and lawmaker, Misa Bharti, 42, accompanied her mother to the income tax office during the questioning around afternoon.
The IT department had earlier attached farm houses, land and buildings in Delhi and Patna, including plots in the Bihar capital where a mall was to be built in this case.
According to investigators, many plots owned by the Yadavs were bought and transferred to the family by firms who were awarded contracts by Lalu when he was the Railways Minister.
In all, six members of the Lalu Yadav family are suspected to have purchased properties in the name of others to conceal who really owns them.
The questioning comes days after Lalu Yadav addressed a joint opposition rally in Patna that targetted the BJP and its new ally, Chief Minister Nitish Kumar. Tax officials, however, pointed that the department had summoned Rabri Devi and Tejashwi Yadav on an earlier date but they had sought some more time.
This was one of the cases that led Bihar Chief Minister Nitish Kumar to terminate the grand alliance with Lalu Yadav's party and the Congress last month, and renewing his partnership with the BJP.
Mr Kumar has hit back at critics of his move to swap partners, saying the "mandate was for serving the people of Bihar and not for enriching one family".