BlackRock, the world's largest asset manager, is to offer some of its institutional fund investors a choice over how their shares are cast at company shareholder meetings — a move that will likely pile pressure on rivals to give asset owners more of a say in the process.

In a letter to clients, seen by Financial News, BlackRock said that institutional investors in certain index strategies will be able to choose how they participate in proxy voting — the process where shareholders, often large investors such as pension funds, delegate the process of vote casting.