The FPO, which opened on Friday, was initially scheduled to close on Tuesday.
The company has cut the price band to Rs 71-77 per share for its FPO from Rs 72-77 per share in the wake of lukewarm response from investors.
The FPO comprises fresh issue of up to 18 crore equity shares. Besides, an additional issue constituting up to 18 lakh shares reserved for employees.
The issue was subscribed 49 per cent on day 3 of the bidding process on Tuesday. It was subscribed just 9 per cent on the second day.
"We have revised our issue period and extended it by three days. The bid/ issue closing date will now be January 31, 2020," ITI said in a statement.
At the upper end of the price band, the company is expected to mop-up Rs 1,400 crore.
Proceeds of the issue will be utilised towards working capital requirements, repayment of loan taken by the company and for general corporate purpose.
The public issue is being managed by BOB Capital Markets Ltd, Karvy Investor Services Ltd and PNB Investment Services.
The FPO will help the company meet markets regulator Securities and Exchange Board of India's (Sebi) requirement of minimum 25 per cent public shareholding.
ITI is into manufacturing of a diverse range of Information and Communication Technology (ICT) products and solutions. Its customers include BSNL, MTNL, defence, paramilitary forces and state governments. SP BAL