Rio Tinto’s bid to complete a takeover of Turquoise Hill Resources has received a boost after the most vocal opponents of the deal agreed not to vote at the shareholder meeting that will determine whether the USD 3.3 billion deal goes ahead.

Rio has owned almost 51 percent of Canadian listed Turquoise Hill for a decade but this year moved to acquire the remaining 49 percent as part of efforts to simplify the ownership structure of Mongolia’s Oyu Tolgoi copper mine.

Turquoise Hill owns 66 percent of Oyu Tolgoi but outsources management of the project to Rio, and that structure has triggered years of acrimony and distrust between the Mongolian government, Rio and minority shareholders in Turquoise Hill.

Two of the most vocal critics of Rio’s involvement in the Mongolian project over the past decade have been Sailingstone Capital Partners and Pentwater Capital Management; both of which have spent time as the second-biggest shareholder in Turquoise Hill and both of which have expressed dissatisfaction with Rio’s $C43 per share takeover offer.

But on Wednesday morning Australian time, Pentwater and Sailingstone agreed to withhold their votes at next week’s meeting of Turquoise Hill shareholders that will determine whether Rio’s bid is successful.

Pentwater and Sailingstone will instead exercise the rights offered by a quirk in Canadian mergers and acquisitions regulations, which allows shareholders in a target company to nominate their shares as “dissenting”.