Institutional Shareholder Services (ISS) is backing activist investor Palliser Capital's proposal to review Rio Tinto Group's (ASX:RIO) dual-listing structure in favor of a unification of the company, media outlets reported Wednesday.

The proxy advisory firm said the unification would bring several benefits such as "reduced complexity and lower chance of conflict of interest, strategic flexibility and, for Plc shareholders, a closing of the valuation discount of their shares," according to an ISS report seen by Reuters.

This comes after Glass Lewis made a similar recommendation, arguing that shareholders deserve more than the "closed-door internal assessment conducted by the Board to date."

Palliser Capital has been urging Rio Tinto to dismantle its dual-listing structure, a proposal that has received pushback from the mining giant.

Rio Tinto London shareholders will vote on Palliser Capital's resolution on April 3, while their Australian counterparts will vote on May 1.

In a Wednesday filing with the Australian bourse, Rio Tinto maintained its unanimous recommendation for shareholders to vote against the resolution. The company said unification would be "value destructive for the group and its shareholders" and that claims of $50 billion of value erosion due to the current structure are "unfounded and misleading."