According to Reuters, the 30% Club UK Investor Group, whose members are, among others, Japan's Government Pension Investment Fund and Aviva Investors, told all FTSE 100 companies that they need to include at least one member who belongs to a minority.
The group refused to make the names of the companies public for now, but said it will name them if they don't comply until the next progress report.
The target for this project was the end of 2021 for FTSE 100 companies and the FTSE 250 ones must comply until 2024.
Board members from companies who refuse to comply risk not being re-elected by their shareholders at the annual meetings.
Diandra Soobiah, co-chair at 30% Club said that "diversity and inclusion in companies are integral to sound corporate governance and corporate culture. As long-term investors, we see the failure to take diversity seriously as a stark warning about the long-term sustainability of the company."