Origin Energy investors have ramped up calls for the electricity supplier’s North American bidders to sweeten their takeover offer after they convinced the Australian Competition and Consumer Commission the $18.7 billion deal would accelerate the flagging energy transition.

The regulator surprised many in the market by waving through the proposed takeover by Canada’s Brookfield and its US-based partner, EIG, on Tuesday with minimal additional conditions, turning the debate to shareholder value in the mega-deal.