The state-run firm's stock crashed 11.9 per cent to Rs 135 in intra-day trade and finally ended 11.26 per cent down at Rs 136 on the BSE. At the NSE, NTPC's stock dipped 11.37 per cent to close at Rs 136.
Following the fall in the stock, the market value of NTPC dropped by Rs 14,223 crore to Rs 1,12,138 crore.
The scrip was the top loser among the blue-chips on both Sensex and Nifty indices.
CERC has issued draft regulations for tariff determination during FY15-19 applicable for government companies.
"We see huge negative impact for NTPC. However, we see lower impact for PGCIL, NHPC and SJVN," brokerage firm Emkay Global said in a report.
"The final regulations could be different from the draft as has happened in the past. However, given the quantum of negative impact is high compared to previous draft regulations even if the norms are relaxed a bit it would still be negative," the report added.
NTPC said it is studying the regulations.
"The draft CERC regulations have just come in public domain and we are studying the same. Prima facie we find positive changes. This paper is under discussion and we are going through with a fine comb before it is finalised. We would like to assure our investors our continued returns and thank them for their support," NTPC said in a statement.
Selling was also seen in other power companies, including NHPC that lost 1.37 per cent, Power Grid Corporation of India shed 3.01 per cent, SJVN (2.88 per cent) and Tata Power (1.52 per cent).