John Thain Adam Jeffery | CNBC

Investor group CtW demanded changes to Uber's board of directors ahead of the ride-hailing company's anticipated IPO, saying on Wednesday its governance "falls short of best practices." In a letter addressed to Uber Chairman Ronald Sugar, CtW called for the removal of former Merrill Lynch executive John Thain from Uber's board, citing his "reputation of poor business judgement on financial matters." The group also said Uber's board members, including its chairman, should reduce their outside commitments ahead of the firm's expected IPO on the New York Stock Exchange in coming weeks. CtW is a union-affiliated pension fund adviser with more than $250 billion in assets under management. The group has previously scrutinized the board practices of companies like Tesla and said in the letter its funds intend to become "substantial" Uber shareholders. The group was highly critical of Thain, who leads Uber's Audit Committee. CtW referenced the former Merrill Lynch chief executive's "close relationship" with Uber CFO Nelson Chai, who worked under Thain at NYSE, Merrill Lynch and CIT Group.

"We believe that Thain's close relationship with Chai may inhibit him from effectively evaluating Chai's performance as CFO and possibly from holding Chai accountable in the event of the company's poor financial performance," the letter said. The group also attacked Thain's business record, which came under scrutiny in early 2009 when he was fired from his role as CEO of Merrill Lynch. Thain oversaw Bank of America's acquisition of the firm for $50 billion in stock and approved large executive bonuses at the peak of the financial crisis. "Thain is an unsuitable steward of shareholder funds," the letter said. Uber did not immediately respond to CNBC's request for comment and CNBC was unable to reach Thain for comment. Thain, who retired as CEO of CIT Group in 2015, also currently sits on the supervisory board of Deutsche Bank.