Markets regulator Sebi is considering if the proposed merger of Aditya Birla Group firm Idea Cellular with Vodafone Plc’s India unit will trigger an open offer, sources said. Securities and Exchange Board of India (Sebi), in May this year, had sought clarification from Idea Cellular on the proposed merger. The Aditya Birla Group company had submitted the scheme of arrangement, or merger plan, to the regulator in April. In March, Vodafone India and Idea Cellular announced the merger of their operations to create the country’s largest mobile phone operator worth more than $23 billion with a 35 per cent market share. As part of the proposal, Vodafone India will initially hold 50 per cent stake in the merged entity. Later, the British firm will own 45.1 per cent of the combined entity while the Aditya Birla group, Idea’s parent company, will hold 26 per cent after paying Rs 3,874 crore for a 4.9 per cent stake. The remaining 28.9 per cent will be held by other shareholders. According to sources, Sebi is examining the possibility if the proposed merger would trigger open offer under ‘takeover’ norms. Under the takeover norms, if an entity acquires 25 per cent stake in a listed firm, it has to make an open offer for an additional 26 per cent from public shareholders.