At issue was the joint investment (with a 70%-30% split) of two private equity funds in a company that contributed to a multiemployer pension plan ("MEP") for its union employees. When the portfolio company went bankrupt a few years later, the MEP assessed withdrawal liability against the funds on the basis of the joint and several liability of controlled group members for MEP withdrawals under the Employee Retirement Income Security Act of 1974, as amended ("ERISA").