The International Corporate Governance Network (ICGN), consisting of investors with more than $90 trillion in combined assets under management, spoke out against the bill on Tuesday. According to its website, ICGN members include Alliance Bernstein, the Swedish AP funds, BlackRock, CalPERS, CalSTRS, Franklin Templeton, Norges and Vanguard.

ICGN CEO Jen Sisson cautioned in a letter sent to Delaware state senators and representatives that SB 21 "will be detrimental to shareholder rights, with potentially significant negative implications for long-term returns for investors, including people saving for their retirements, current retirees and other individuals investing their savings."

Sisson also said the bill would "reduce judicial oversight" and diminish shareholders' trust that they can "seek remedies through litigation, when necessary."