Tata Sons will buy about 83.6 million shares in Tata Motors at or around the prevailing price of the stock on the date of the planned acquisition, it said in the filing.
It cited "restructuring of investment portfolio" as the reason for the planned deal.
Tata Motors shares closed at 455.75 rupees in Mumbai trading on Friday.
Tata Sons owned 28.71 percent of Tata Motors at the end of March, while Tata Steel owned 2.9 percent in the vehicle maker.
Tata Sons owned 29.75 percent of Tata Steel at the end of March, while Tata Motors owned a 0.46 percent stake in the steelmaker, according to stock exchange data.
Indian media have reported that Tata Sons planned to reduce crossholdings among group companies.
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