Cazenove Capital and Schroders Wealth Management combined are responsible for £62bn of assets, with £29bn invested in collective investment funds.
The firm has written to 93 of these fund managers, who in aggregate control over £30trn of assets, to set out its view on voting best practice.
The letter, seen by FTAdviser, said: "As a significant investor in third-party funds, we have a role to play in encouraging change across the wider investment industry. As part of our engagement with managers, we believe it is important to share what we consider to be the most effective ways of promoting more sustainable business practices within financial markets and among participants.
"As AGM season gets underway, we are writing to all our managers who are able to vote to highlight our key recommendations with regards to voting."
The firm said it believes that best practice on voting includes the following:
Meeting these recommendations ensures managers are not just talking about sustainability and ESG but are actually taking demonstrable action, it said.
Chloe Mallo, investment manager at Cazenove Capital, said: “Fund managers should be using their votes to hold the underlying companies in which they invest to account on ESG issues.
“Our letter clearly sets out our interpretation of best practice.
“We have committed to this approach for the investments we hold directly on behalf of our clients. We encourage managers that we work with to do the same.”
The firm said this public letter is a first and demonstrates the important role the sector can play in steering the broader industry towards best practice in sustainable investment.
It said collective investment funds constitute a significant share of its investments on behalf of individuals, family offices, endowments and charities.
“This puts us – and other wealth managers – in a powerful position to drive change throughout the asset management industry,” the firm said.