Two additional UK investors on Monday joined the Rockefeller family effort to force ExxonMobil, the world’s biggest private oil company, to support an independent chairman.

The announcement concerning Universities Superannuation Scheme, the UK’s third-largest pension fund, and Railpen Investments, the seventh-largest UK pension fund, came one day after four other leading UK investors said they would support the proxy measure to split the functions of Rex Tillerson as chief executive and chairman at Exxon’s annual meeting on May 28.