The trading activities of these entities came to the notice of the regulator on May 16, the day results of the Lok Sabha elections were declared.
To prevent possible manipulations and excessive volatility in stock trading in the wake of election results, the Securities and Exchange Board of India (Sebi) had made elaborate mechanism to keep a close tab on the market.
Sources said that more than 30 entities have come under the scanner after Sebi noticed unusual trading volumes pertaining to them on May 16.
A preliminary enquiry has been initiated to ascertain whether these entities, that includes brokers and high net worth individuals, indulged in suspicious transactions, they added.
The market regulator is gathering information about such transactions from its Integrated Market Surveillance System (IMSS). Besides, data is being collated from the exchanges and clearing corporations, among others, sources said.
A special team at Sebi kept a close tab on the stock market movements, while another team monitored the election results as they were announced to understand whether price movements are linked to outcomes in various constituencies. Sebi would also be closely watching market movements on Monday to avert any possible shocks.
Earlier sources had said that trends in overseas markets and factors affecting foreign institutional investors were also being monitored continuously. On May 16, the 30-share Sensex, which had gained over 1,560 points in five sessions previously, had surged 1,470 points before closing at a new peak of 24,121.74 points.