"We have sent a legal notice to the directors of Larsen & Toubro," she told Reuters on Tuesday, refusing to give details.
She was responding to a newspaper report that Grasim had objected to the spin-off plan.
Grasim, part of India's Aditya Birla group, has invested more than Rs 10 billion (Rs 1000 crore) in buying a little over 15 per cent in number-two cement maker L&T.
In October, it made a bid to buy a further 20 per cent in L&T to consolidate its cement business. Analysts say the hive off by bringing in a new partner would stall Grasim's plans.
Grasim, India's third-largest cement producer, also makes viscose staple fibre, textiles, caustic soda and sponge iron.
Grasim's bid is in a limbo after the Securities and Exchange Board of India last month imposed a stay, pending investigation into a possible violation of takeover rules by Grasim. The offer had been due to open on Monday.
The Economic Times said on Tuesday that Grasim's notice asked the L&T management to defer the demerger proposal as Grasim's open offer was alive "in fact and in law" and that proceeding with the plan would expose the management to prolonged litigation.
L&T officials were not available for comment.
The engineering and construction company had mooted a plan to hive off the cement division two years ago, but L&T failed to clinch a partner for the unit despite initial interest from some foreign bidders.
The plan appeared to have taken a backseat after Grasim invested in the firm in November 2001, buying little over 10 per cent from petrochemicals giant Reliance Industries Ltd.
Last month, after Grasim announced plans to raise its holdings, L&T said a committee was looking into an investment proposal for the unit.
L&T officials are tight-lipped on the proposal though media reports speculated that private equity fund Commonwealth Development Corporation aimed to pick up a six per cent stake.
L&T's shares, which traded at Rs 197.9 in the afternoon, are up about three per cent since Grasim's open offer was stayed, while Grasim has lost about six per cent to Rs 296.25.
