While a company spokesperson did not comment on queries related to the notice, sources said SEBI had begun the probe in early 2008 after issue was raised in Parliament.
RIL had sold over four per cent equity in RPL in November 2007, prior to which heavy selling, said to be by various group entities, was noticed in the futures contract of RPL.
Sources said the gains made through these transactions could be over Rs 500 crore (Rs but no confirmation could be obtained from SEBI.
In the show-cause notice, SEBI is understood to have asked RIL and 12 associate entities, who said to have sold in the futures market, why action should not be taken against them under the SEBI Act and the Prevention of Fraudulent and Unfair Practices Regulation.
When contacted, SEBI's investigation department officials did not comment, saying they were not authorised to speak to media, while SEBI spokesperson could not be contacted.